Mizuho Financial (MFG) 20-F 25 Jul 14 2014 FY Annual report (foreign) Financial data

Document_and_Entity_Informatio

Document and Entity Information	12 Months Ended
	Mar. 31, 2014
Document Type	'20-F
Amendment Flag	'false
Document Period End Date	31-Mar-14
Document Fiscal Year Focus	'2014
Document Fiscal Period Focus	'FY
Trading Symbol	'MFG
Entity Registrant Name	'MIZUHO FINANCIAL GROUP INC
Entity Central Index Key	'0001335730
Current Fiscal Year End Date	'--03-31
Entity Well-known Seasoned Issuer	'Yes
Entity Current Reporting Status	'Yes
Entity Filer Category	'Large Accelerated Filer
Entity Common Stock, Shares Outstanding	24,263,885,187

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, unless otherwise specified
Assets:	'	'
Cash and due from banks	¥ 1,696,879	¥ 1,268,442
Interest-bearing deposits in other banks	19,037,527	11,215,597
Call loans and funds sold	468,283	530,542
Receivables under resale agreements (Note 29)	8,349,365	9,024,808
Receivables under securities borrowing transactions (Note 29)	5,010,740	5,543,914
Trading account assets	27,408,259	34,066,555
Investments:	'	'
Available-for-sale securities (including assets pledged that secured parties are permitted to sell or repledge of ¥6,549,038 million in 2013 and ¥3,422,827 million in 2014)	30,648,761	39,413,951
Held-to-maturity securities	4,040,083	3,000,403
Other investments	792,689	838,135
Loans (Notes 4, 5, 8 and 28)	73,484,954	69,833,483
Allowance for loan losses	-626,177	-772,957
Loans, net of allowance	72,858,777	69,060,526
Premises and equipment-net (Note 6)	1,356,594	1,091,989
Due from customers on acceptances	92,398	101,590
Accrued income	264,380	276,193
Goodwill (Note 7)	11,549	6,147
Intangible assets (Note 7)	58,947	64,474
Deferred tax assets (Note 19)	405,120	641,777
Other	3,198,995	2,601,951
Total	175,699,346	178,746,994
Liabilities and equity:	'	'
Noninterest-bearing deposits	12,751,194	12,138,640
Interest-bearing deposits	73,114,857	74,218,101
Noninterest-bearing deposits	1,114,729	836,177
Interest-bearing deposits	15,629,374	13,028,638
Due to trust accounts (Note 10)	742,036	619,271
Call money and funds purchased	7,194,433	6,126,425
Payables under repurchase agreements (Note 29)	16,797,809	17,451,080
Payables under securities lending transactions (Note 29)	6,265,875	11,496,178
Other short-term borrowings	6,023,972	6,724,100
Trading account liabilities	14,824,922	16,768,830
Bank acceptances outstanding	92,398	101,590
Income taxes payable	57,124	37,555
Deferred tax liabilities (Note 19)	33,181	14,301
Accrued expenses	160,107	158,664
Long-term debt	9,853,941	8,802,223
Other	4,422,023	4,368,126
Total	169,077,975	172,889,899
Commitments and contingencies (Note 23)	'	'
MHFG shareholders' equity:	'	'
Preferred stock (Note 13)	312,651	377,354
Common stock (Note 14)-no par value, authorized 48,000,000,000 shares in 2013 and 2014, and issued 24,164,864,477 shares in 2013, and 24,263,885,187 shares in 2014	5,489,295	5,460,821
Accumulated deficit	-537,479	-883,390
Accumulated other comprehensive income, net of tax (Note 16)	1,117,877	777,997
Less: Treasury stock, at cost-Common stock 22,128,230 shares in 2013, and 13,817,747 shares in 2014	-3,874	-4,662
Total MHFG shareholders' equity	6,378,470	5,728,120
Noncontrolling interests (Note 24)	242,901	128,975
Total equity	6,621,371	5,857,095
Total	175,699,346	178,746,994
Consolidated VIEs	'	'
Assets:	'	'
Cash and due from banks	25,762	15,078
Interest-bearing deposits in other banks	10,306	3,216
Trading account assets	1,383,280	936,800
Investments:	'	'
Investments	72,626	83,762
Loans, net of allowance	2,639,153	2,428,898
Other	421,585	343,522
Total	4,552,712	3,811,276
Liabilities and equity:	'	'
Other short-term borrowings	287,910	253,311
Trading account liabilities	7,355	10,585
Long-term debt	173,870	144,055
Other	929,990	978,685
Total	¥ 1,399,125	¥ 1,386,636

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, except Share data, unless otherwise specified
Trading account assets, assets pledged that secured parties are permitted to sell or repledge	¥ 9,445,432	¥ 12,090,161
Available-for-sale securities, assets pledged that secured parties are permitted to sell or repledge	3,422,827	6,549,038
Long-term debt, liabilities accounted for at fair value	¥ 657,626	¥ 552,354
Common stock, par value	¥ 0	¥ 0
Common stock, authorized	48,000,000,000	48,000,000,000
Common stock, issued	24,263,885,187	24,164,864,477
Treasury stock, shares	13,817,747	22,128,230

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (JPY ¥)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Interest and dividend income:	'		'		'
Loans, including fees	¥ 982,402		¥ 947,983		¥ 936,574
Investments:	'		'		'
Interest	131,295		162,451		170,651
Dividends	72,052		63,329		71,579
Trading account assets	161,212		169,216		193,288
Call loans and funds sold	5,949		4,947		6,601
Receivables under resale agreements and securities borrowing transactions	36,281		57,220		39,684
Deposits	33,608		18,229		18,709
Total interest and dividend income	1,422,799		1,423,375		1,437,086
Interest expense:	'		'		'
Deposits	133,140		124,053		131,140
Debentures	'		'		385
Trading account liabilities	30,746		23,688		28,436
Call money and funds purchased	7,664		7,686		8,604
Payables under repurchase agreements and securities lending transactions	36,906		66,995		47,114
Other short-term borrowings	12,120		16,490		20,481
Long-term debt	180,989		173,939		179,799
Total interest expense	401,565		412,851		415,959
Net interest income	1,021,234		1,010,524		1,021,127
Provision (credit) for loan losses (Notes 4 and 5)	-126,230		139,947		-23,044
Net interest income after provision (credit) for loan losses	1,147,464		870,577		1,044,171
Noninterest income:	'		'		'
Fees and commissions (Note 26)	675,763		612,808		575,413
Foreign exchange gains (losses)-net (Note 27)	25,631	[1]	20,514	[1]	98,054	[1]
Trading account gains (losses)-net (Note 27)	-59,687		534,100		333,315
Investment gains (losses)-net (Note 3)	265,531		121,159		-32,991
Gains on disposal of premises and equipment	10,460		12,411		19,924
Other noninterest income (Note 22)	165,136		138,427		96,420
Total noninterest income	1,082,834		1,439,419		1,090,135
Noninterest expenses:	'		'		'
Salaries and employee benefits (Note 20)	586,737		572,301		587,332
General and administrative expenses	486,772		439,708		477,512
Impairment of goodwill (Note 7)	3,792		'		5,637
Occupancy expenses	172,566		171,697		174,788
Fees and commission expenses	122,419		109,018		107,898
Provision (credit) for losses on off-balance-sheet instruments (Note 23)	12,095		4,584		-1,203
Other noninterest expenses (Notes 4 and 22)	119,574		127,508		119,507
Total noninterest expenses	1,503,955		1,424,816		1,471,471
Income before income tax expense	726,343		885,180		662,835
Income tax expense (Note 19)	226,108		4,024		13,878
Net income	500,235		881,156		648,957
Less: Net income (loss) attributable to noncontrolling interests	1,751		5,744		-7,432
Net income attributable to MHFG shareholders	¥ 498,484		¥ 875,412		¥ 656,389
Earnings per common share (Note 18):	'		'		'
Basic net income per common share	¥ 20.33		¥ 36.05		¥ 28.07
Diluted net income per common share	¥ 19.64		¥ 34.47		¥ 26.78
[1]	Amounts include realized and unrealized gains and losses on both derivative instruments and nonderivative instruments, such as translation gains and losses related to foreign currency-denominated available-for-sale securities for which the fair value option is elected in accordance with ASC 825.

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Net income	¥ 500,235	¥ 881,156	¥ 648,957
Other comprehensive income (loss), net of tax:	'	'	'
Unrealized net gains (losses) on available-for-sale securities, net of tax (Note 3)	137,128	368,896	105,285
Foreign currency translation adjustments, net of tax	76,104	87,651	-7,814
Pension liability adjustments, net of tax (Note 20)	136,942	78,676	39,687
Total other comprehensive income (loss), net of tax	350,174	535,223	137,158
Total comprehensive income	850,409	1,416,379	786,115
Less: Total comprehensive income (loss) attributable to noncontrolling interests	12,045	8,558	-10,570
Total comprehensive income attributable to MHFG shareholders	¥ 838,364	¥ 1,407,821	¥ 796,685

CONSOLIDATED_STATEMENTS_OF_EQU

CONSOLIDATED STATEMENTS OF EQUITY (JPY ¥)	Total		Preferred stock (Note 13):	Common stock (Note 14):	Accumulated deficit:	Accumulated other comprehensive income, net of tax (Note 16):	Treasury stock, at cost:	Total MHFG shareholders' equity	Noncontrolling interests:
In Millions
Balance at beginning of fiscal year at Mar. 31, 2011	'		¥ 453,576	¥ 5,164,160	¥ (2,046,024)	¥ 104,972	¥ (3,197)	'	¥ 361,869
Issuance of new shares of common stock for stock exchanges (Note 14)	'		'	244,100	'	'	'	'	'
Purchases of treasury stock	'		'	'	'	'	-2,560	'	'
Net income	648,957		'	'	656,389	'	'	'	'
Conversion to common stock	'		-43,208	'	'	'	'	'	'
Change during year	140,616		'	'	'	140,616	'	'	'
Issuance of new shares of common stock by conversion of preferred stock	'		'	43,208	'	'	'	'	'
Disposal of treasury stock	'		'	'	'	'	12,001	'	'
Dividends declared	-216,508	[1],[2]	'	'	-216,473	'	'	'	'
Effect of stock exchanges (Note 14)	'		'	'	'	'	-13,318	'	-216,558
Gains (losses) on disposal of treasury stock	'		'	-48	'	'	'	'	'
Effect of other increase/decrease in consolidated subsidiaries	'		'	'	'	'	'	'	65,183
Stock-based compensation (Note 21)	'		'	106	'	'	'	'	'
Dividends paid to noncontrolling interests	'		'	'	'	'	'	'	-23,666
Change in ownership interest in consolidated subsidiaries	'		'	-23,534	'	'	'	'	'
Net income (loss) attributable to noncontrolling interests	7,432		'	'	'	'	'	'	-7,432
Unrealized net gains (losses) on available-for-sale securities attributable to noncontrolling interests	'		'	'	'	'	'	'	-2,044
Foreign currency translation adjustments attributable to noncontrolling interests	'		'	'	'	'	'	'	-1,353
Pension liability adjustments attributable to noncontrolling interests	'		'	'	'	'	'	'	259
Balance at end of fiscal year at Mar. 31, 2012	4,647,024		410,368	5,427,992	-1,606,108	245,588	-7,074	4,470,766	176,258
Purchases of treasury stock	'		'	'	'	'	-395	'	'
Net income	881,156		'	'	875,412	'	'	'	'
Conversion to common stock	'		-33,014	'	'	'	'	'	'
Change during year	532,409		'	'	'	532,409	'	'	'
Issuance of new shares of common stock by conversion of preferred stock	'		'	33,014	'	'	'	'	'
Disposal of treasury stock	'		'	'	'	'	2,807	'	'
Dividends declared	-152,722	[2]	'	'	-152,694	'	'	'	'
Gains (losses) on disposal of treasury stock	'		'	-631	'	'	'	'	'
Effect of other increase/decrease in consolidated subsidiaries	'		'	'	'	'	'	'	-36,457
Stock-based compensation (Note 21)	'		'	529	'	'	'	'	'
Dividends paid to noncontrolling interests	'		'	'	'	'	'	'	-19,384
Change in ownership interest in consolidated subsidiaries	'		'	-83	'	'	'	'	'
Net income (loss) attributable to noncontrolling interests	-5,744		'	'	'	'	'	'	5,744
Unrealized net gains (losses) on available-for-sale securities attributable to noncontrolling interests	'		'	'	'	'	'	'	2,408
Foreign currency translation adjustments attributable to noncontrolling interests	'		'	'	'	'	'	'	190
Pension liability adjustments attributable to noncontrolling interests	'		'	'	'	'	'	'	216
Balance at end of fiscal year at Mar. 31, 2013	5,857,095		377,354	5,460,821	-883,390	777,997	-4,662	5,728,120	128,975
Purchases of treasury stock	'		'	'	'	'	-37,387	'	'
Net income	500,235		'	'	498,484	'	'	'	'
Conversion to common stock	'		-28,013	'	'	'	'	'	'
Change during year	339,880		'	'	'	339,880	'	'	'
Issuance of new shares of common stock by conversion of preferred stock	'		'	28,013	'	'	'	'	'
Disposal of treasury stock	'		'	'	'	'	1,177	'	'
Dividends declared	-152,265	[2]	'	'	-152,265	'	'	'	'
Gains (losses) on disposal of treasury stock	'		'	-31	'	'	'	'	'
Effect of other increase/decrease in consolidated subsidiaries	'		'	'	'	'	'	'	113,887
Stock-based compensation (Note 21)	'		'	492	'	'	'	'	'
Cancellation of treasury stock	'		'	'	'	'	36,998	'	'
Cancellation of preferred stock	'		-36,690	'	-308	'	'	'	'
Dividends paid to noncontrolling interests	'		'	'	'	'	'	'	-12,006
Net income (loss) attributable to noncontrolling interests	-1,751		'	'	'	'	'	'	1,751
Unrealized net gains (losses) on available-for-sale securities attributable to noncontrolling interests	'		'	'	'	'	'	'	8,980
Foreign currency translation adjustments attributable to noncontrolling interests	'		'	'	'	'	'	'	118
Pension liability adjustments attributable to noncontrolling interests	'		'	'	'	'	'	'	1,196
Balance at end of fiscal year at Mar. 31, 2014	¥ 6,621,371		¥ 312,651	¥ 5,489,295	¥ (537,479)	¥ 1,117,877	¥ (3,874)	¥ 6,378,470	¥ 242,901
[1]	As MHFG commenced distributing an interim dividend from the fiscal year ended March 31, 2012, the amounts for the fiscal year include such interim dividends.
[2]	Dividends paid on treasury stock are excluded.

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities:	'	'	'
Net income	¥ 500,235	¥ 881,156	¥ 648,957
Less: Net income (loss) attributable to noncontrolling interests	1,751	5,744	-7,432
Net income attributable to MHFG shareholders	498,484	875,412	656,389
Adjustments to reconcile net income to net cash provided by (used in) operating activities:	'	'	'
Depreciation and amortization	161,258	157,165	165,721
Provision (credit) for loan losses	-126,230	139,947	-23,044
Investment losses (gains)-net	-265,531	-121,159	32,991
Foreign exchange losses (gains)-net	127,254	160,588	-5,747
Deferred income tax expense (benefit)	90,375	-43,831	-40,939
Net change in trading account assets	7,205,841	-2,336,912	-2,953,353
Net change in trading account liabilities	-2,359,775	-536,213	329,761
Net change in loans held for sale	-53,291	4,571	3,860
Net change in accrued income	21,735	-22,386	-9,321
Net change in accrued expenses	12,262	-20,215	15,286
Other-net	638,926	445,045	38,965
Net cash provided by (used in) operating activities	5,951,308	-1,297,988	-1,789,431
Cash flows from investing activities:	'	'	'
Proceeds from sales of investments	64,003,905	75,617,212	69,659,407
Proceeds from maturities of investments	9,862,926	14,578,614	15,079,088
Purchases of investments	-65,822,738	-89,109,906	-87,496,663
Proceeds from sales of loans	215,419	144,244	224,957
Net change in loans	-2,313,291	-2,501,863	-1,703,880
Net change in interest-bearing deposits in other banks	-7,417,572	-4,638,673	2,074,843
Net change in call loans and funds sold, and receivables under resale agreements and securities borrowing transactions	2,306,310	-268,103	480,641
Proceeds from sales of premises and equipment	39,324	18,002	13,231
Purchases of premises and equipment	-456,980	-161,359	-174,517
Net cash provided by (used in) investing activities	417,303	-6,321,832	-1,842,893
Cash flows from financing activities:	'	'	'
Net change in deposits	657,308	7,417,964	2,109,866
Net change in debentures	'	'	-740,933
Net change in call money and funds purchased, and payables under repurchase agreements and securities lending transactions	-6,771,338	7,468,344	3,594,469
Net change in due to trust accounts	122,765	59,537	-69,662
Net change in other short-term borrowings	-724,788	-7,251,033	-1,261,955
Proceeds from issuance of long-term debt	1,999,764	1,602,983	1,052,849
Repayment of long-term debt	-1,097,627	-1,488,151	-1,479,148
Proceeds from noncontrolling interests	43,083	1,057	627
Payment to noncontrolling interests	-1	-11	-107
Proceeds from issuance of common stock	'	'	5
Proceeds from sales of treasury stock	11	1,074	1,961
Purchases of treasury stock	-37,013	-7	-2,560
Dividends paid	-152,163	-152,514	-215,902
Dividends paid to noncontrolling interests	-12,006	-19,384	-23,666
Net cash provided by (used in) financing activities	-5,972,005	7,639,859	2,965,844
Effect of exchange rate changes on cash and due from banks	31,831	31,776	-1,424
Net increase (decrease) in cash and due from banks	428,437	51,815	-667,904
Cash and due from banks at beginning of fiscal year	1,268,442	1,216,627	1,884,531
Cash and due from banks at end of fiscal year	1,696,879	1,268,442	1,216,627
Supplemental disclosure of cash flow information:	'	'	'
Interest paid	408,803	447,766	427,104
Income taxes paid (refunded), net	122,619	92,547	40,211
Noncash investing activities:	'	'	'
Transfer from loans into other investments	'	'	1,351
Investment in capital leases	7,901	8,547	2,985
Noncash acquisition of noncontrolling interests in stock exchanges (Note 14)	'	'	¥ 216,558

Basis_of_presentation_and_summ

Basis of presentation and summary of significant accounting policies	12 Months Ended
	Mar. 31, 2014
Basis of presentation and summary of significant accounting policies	'
	1. Basis of presentation and summary of significant accounting policies
	Basis of presentation
	Mizuho Financial Group, Inc. (“MHFG”) is a joint stock corporation with limited liability under the laws of Japan. MHFG, through its subsidiaries (“the MHFG Group”, or “the Group”), provides domestic and international financial services in Japan and other countries. MHFG’s subsidiaries are segmented on the basis of the nature of the financial products and services. Mizuho Bank, Ltd. (“MHBK”) is a banking subsidiary and offers a wide range of financial products and services mainly in relation to deposits, lending and exchange settlement to individuals, small and medium enterprises (“SMEs”), large corporations, financial institutions, public sector entities and foreign corporations, including foreign subsidiaries of Japanese corporations. Mizuho Trust & Banking Co., Ltd. (“MHTB”) is a trust bank subsidiary and offers mainly trust-related products and consulting services. Mizuho Securities Co., Ltd. (“MHSC”) is a securities and investment banking subsidiary and offers full-line securities services to corporations, financial institutions, public sector entities and individuals. Other major subsidiaries include Trust & Custody Services Bank, Ltd. (“TCSB”), Mizuho Capital Co., Ltd., and Mizuho Business Financial Center Co., Ltd. See Note 31 “Business segment information” for further discussion of the Group’s segment information.
	The accompanying consolidated financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (“U.S. GAAP”). The consolidated financial statements are stated in Japanese yen, the currency of the country in which MHFG is incorporated and principally operates.
	The accompanying consolidated financial statements include the accounts of MHFG and its subsidiaries. MHFG’s fiscal year ends on March 31 and fiscal year of certain subsidiaries ends on December 31. The necessary adjustments have been made to the consolidated financial statements if significant intercompany transactions took place during the three-months periods. When determining whether to consolidate investee entities, we performed a careful analysis of the facts and circumstances of a particular relationship among entities as well as ownership of voting shares. The consolidated financial statements also include the accounts of the VIEs for which MHFG or its subsidiaries have been determined to be the primary beneficiary under the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 810, “Consolidation” (“ASC 810”). All significant intercompany transactions and balances have been eliminated in consolidation. The MHFG Group accounts for investments in entities over which it has significant influence using the equity method of accounting. These investments are included in Other investments and the Group’s proportionate share of income or loss is included in Investment gains (losses)—net.
	Use of estimates
	The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect reported amounts and related disclosures. Specific areas, among others, requiring the application of management’s estimates and judgment include assumptions pertaining to the allowance for loan losses, allowance for losses on off-balance-sheet instruments, deferred tax assets, derivative financial instruments, investments and pension and other employee benefits. Actual results could differ from estimates and assumptions made.
	Definition of cash and due from banks
	For purposes of the consolidated statements of cash flows, Cash and due from banks include cash on hand, cash items in the process of collection and noninterest-bearing deposits with banks.
	Translation of foreign currency financial statements and foreign currency transactions
	Financial statements of overseas entities are prepared using the functional currency of each entity and translated into Japanese yen for consolidation purposes. Assets and liabilities are translated using the fiscal-year-end exchange rate of each functional currency, and income and expense using the average rate of each functional currency for the period.
	Foreign currency translation gains and losses related to the financial statements of overseas entities of the MHFG Group, net of related income tax effects, are credited or charged directly to Foreign currency translation adjustments, a component of Accumulated other comprehensive income (loss), net of tax (“AOCI”). The tax effects of gains and losses related to the foreign currency translation of financial statements of overseas entities are not recognized unless it is apparent that the temporary differences will reverse in the foreseeable future.
	Assets and liabilities denominated in foreign currencies are translated into Japanese yen at the fiscal-year-end foreign exchange rates, and gains and losses resulting from such translation are included in Foreign exchange gains (losses)—net, as appropriate. Foreign currency denominated income and expenses are translated using the average exchange rates for the period.
	Call loans and call money
	Call loans and call money represent lending/borrowing through the Japanese short-term money market to/from other financial institutions such as banks, insurance companies, and securities brokerage houses.
	Repurchase and resale agreements, securities lending and borrowing and other secured financing transactions
	Securities sold under agreements to repurchase (“repurchase agreements”), securities purchased under agreements to resell (“resale agreements”) and securities lending and borrowing transactions are accounted for as secured financing or lending transactions when control over the underlying securities is not deemed to be surrendered by the transferor. Otherwise, they are recorded as sales of securities with related forward repurchase commitments or purchases of securities with related forward resale commitments in accordance with ASC 860, “Transfers and Servicing” (“ASC 860”).
	Repurchase transactions where the maturity of the security transferred as collateral matches the maturity of the repurchase agreements (“repo-to-maturity transactions”) are accounted for as sales rather than collateralized financings where the criteria for derecognition of the securities transferred under ASC 860 are met. There were no such transactions accounted for as sales as of March 31, 2013 and 2014.
	Under resale agreements, securities borrowing and certain derivatives transactions, the MHFG Group receives collateral in the form of securities. In many cases, the MHFG Group is permitted to sell or repledge the securities obtained as collateral. Disclosures of such collateral are presented in Note 8 “Pledged assets and collateral”. With respect to repurchase agreements, securities lending, and certain derivative transactions, counterparties may have the right to sell or repledge securities that the MHFG Group has pledged as collateral. The MHFG Group separately discloses these pledged securities in the consolidated balance sheets.
	The MHFG Group monitors credit exposure arising from resale agreements, repurchase agreements, securities borrowing and securities lending transactions on a daily basis, and additional collateral is obtained from or returned to counterparties, as appropriate.
	Trading securities and trading securities sold, not yet purchased
	Trading securities consist of securities and money market instruments that are bought and held principally for the purpose of reselling in the near term with the objective of generating profits on short-term fluctuations in price. Trading securities sold, not yet purchased, are securities and money market instruments sold to third parties that the MHFG Group does not own and is obligated to purchase at a later date to cover the short position. Trading securities and trading securities sold, not yet purchased, are recorded on the trade date. Trading securities and trading securities sold, not yet purchased, are recorded at fair value in the consolidated balance sheets in Trading account assets and Trading account liabilities with realized and unrealized gains and losses recorded on a trade date basis in Trading account gains (losses)—net in the consolidated statements of income. Interest and dividends on trading securities, including securities sold, not yet purchased, are recorded in Interest and dividend income or Interest expense on an accrual basis.
	Investments
	Debt securities that the MHFG Group has both the positive intent and ability to hold to maturity are classified as Held-to-maturity securities and carried at amortized cost. Debt securities that the MHFG Group may not hold to maturity and any marketable equity securities, other than those classified as trading securities, are classified as Available-for-sale securities, and are carried at fair value, with unrealized gains and losses reported in AOCI.
	The credit component of an other-than-temporary impairment of a debt security is reported in Investment gains (losses)—net and the noncredit component is reported in Other comprehensive income (loss). See Note 3 “Investments” for further discussion of impairment. Interest and dividends, as well as amortization of premiums and accretion of discounts, are reported in Interest and dividend income. Amortization of premiums and accretion of discounts on debt securities are recognized over the remaining maturity under the interest method. Gains and losses on disposition of investments are computed using the first-in first-out method for debt securities and the average method for equity securities, and are recorded on the trade date.
	Other investments include marketable and non-marketable equity securities accounted for using the equity method, marketable and non-marketable investments held by consolidated investment companies carried at fair value under specialized industry accounting principles for investment companies, and other non-marketable equity securities carried at cost, less other-than-temporary impairment, if any.
	Derivative financial instruments
	Derivative financial instruments are bought and held principally for the purpose of market making for customers, proprietary trading in order to generate trading revenues and fee income, and also to manage the MHFG Group’s exposure to interest rate, credit and market risks related to asset and liability management. Such derivative financial instruments include interest rate, foreign currency, equity, commodity and credit default swap agreements, options, caps and floors, and financial futures and forward contracts.
	Derivatives bought and held for trading purposes are recorded in the consolidated balance sheets at fair value in Trading account assets and Trading account liabilities. The fair value of derivatives in a gain position and a loss position are reported as Trading account assets and Trading account liabilities, respectively.
	Derivatives used for asset and liability management include contracts that qualify for hedge accounting under ASC 815, “Derivatives and Hedging” (“ASC 815”). To be eligible for hedge accounting, derivative instruments must be highly effective in achieving offsetting changes in fair values or variable cash flows of the hedged items attributable to the particular risk being hedged. All qualifying hedging derivatives are valued at fair value and included in Trading account assets or Trading account liabilities. Derivatives that do not qualify for hedge accounting under ASC 815 are treated as trading positions and are accounted for as such. The fair value amounts recognized for such derivatives are not offset against the amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral under master netting agreement with the same counterparty.
	The fair value of derivative financial instruments is determined based on quoted market prices or broker-dealer quotes, if available. If not, the fair value is estimated using quoted market prices for similar instruments, option or binomial pricing models or a present value cash flow analysis, utilizing current observable market information, where available. In determining the fair value, the Group considers various factors such as exchange or over-the-counter market quotes, time value of money and volatility factors for options and warrants, observed prices for similar or synthetic instruments, and counterparty credit quality including potential exposure.
	Changes in the fair value of all derivatives are recorded in earnings, except for derivatives qualifying as net investment hedges under ASC 815 which are recorded in AOCI. The changes in the fair values of all derivatives relating to foreign currency exchange rates are included in Foreign exchange gains (losses)—net and Trading account gains (losses)—net. Other elements of the changes in the fair values, including interest rate, equity and credit related components except that of certain credit derivatives hedging the credit risk in the corporate loan portfolio, are recognized in Trading account gains (losses)—net. The net gain (loss) resulting from changes in the fair values of certain credit derivatives where the Group purchases protection to mitigate its credit risk exposure related to its corporate loan portfolio is recorded in Other noninterest income (expenses).
	Certain financial and hybrid instruments often contain embedded derivative instruments that possess implicit or explicit contract terms similar to those of a derivative instrument. Such derivative instruments are required to be fair-valued separately from the host contracts if they meet the bifurcation criteria of an embedded derivative. Such criteria include whether the entire instrument is not marked to market through earnings, the economic characteristics and risks of the embedded contract terms are not clearly and closely related to those of the host contract and the embedded contract terms would meet the definition of a derivative on a stand-alone basis.
	Loans
	Loans are generally carried at the principal amount adjusted for unearned income and deferred net nonrefundable loan fees and costs. Loan origination fees, net of certain direct origination costs are deferred and recognized over the contractual life of the loan as an adjustment of yield using a method that approximates the interest method. Interest income on performing loans is accrued and credited to income as it is earned. Unearned income and discounts or premiums on purchased loans are deferred and recognized over the life of the loan using a method that approximates the interest method.
	Loans are considered impaired when, based on current information and events, it is probable that the MHFG Group will be unable to collect all the scheduled payments of principal and interest when due according to the contractual terms of the loan. Factors considered by management in determining if a loan is impaired include delinquency status and the ability of the debtor to make payment of the principal and interest when due. Impaired loans include loans past due for 90 days or more and restructured loans that meet the definition of troubled debt restructuring (“TDR”) in accordance with ASC 310 “Receivables” (“ASC 310”).
	All of the MHFG Group’s impaired loans are designated as nonaccrual loans and thus interest accrual and amortization of net origination fees are suspended and capitalized interest is written off. Cash received on nonaccrual loans is accounted for as reduction of the loan principal if the ultimate collectibility of the principal amount is uncertain, otherwise, as interest income. Loans are not restored to accrual status until interest and principal payments are current and future payments are reasonably assured. Impaired loans return to non-impaired loans and accrual status, when the MHFG Group determines that the borrower poses no problems regarding current certainty of debt fulfillment. In general, such determination is made if the borrower qualifies for an obligor rating of E2 or above and is not classified as a special attention obligor. With respect to loans restructured in TDR, in general, such loans return to non-impaired loans, and accrual status, when the borrower qualifies for an obligor rating of D or above. See Note 4 “Loans” for the definitions of obligor ratings.
	Loans that have been identified to be sold are classified as loans held for sale within Other assets and are accounted for at the lower of cost or fair value on an individual loan basis. If management decides to retain certain loans held for sale for the foreseeable future or until maturity or payoff, such items are transferred to Loans at the lower of cost or fair value.
	Securitization
	The MHFG Group engages in securitization activities related to mortgage loans and other loans in the normal course of business. The MHFG Group records a loan securitization as a sale when the transferred loans are legally isolated from the Group’s creditors and the accounting criteria for a sale are met in accordance with ASC 860. Otherwise, the transfer is accounted for as a collateralized borrowing.
	Allowance and provision (credit) for loan losses
	The MHFG Group maintains an appropriate amount of allowance for loan losses to absorb probable losses inherent in the loan portfolio and makes adjustments to such allowance through the Provision (credit) for loan losses in the consolidated statements of income. Loan principal that management judges to be uncollectible, based on detailed loan reviews and a credit quality assessment, is charged off against the allowance for loan losses. In general, the MHFG Group charges off loans when the Group determines that the debtor should be classified as substantially bankrupt or bankrupt. See Note 4 “Loans” for the definitions of obligor categories. Obligors classified in the retail portfolio segment are generally determined to be substantially bankrupt when they are past due for more than six months, and as for other obligors, the Group separately monitors the credit quality of each obligor without using time-based triggers. Subsequent recoveries of previously charged-off loan balances are recorded as an increase to the allowance for loan losses as the recoveries are received.
	The credit quality review process and the credit rating process serve as the basis for determining the allowance for loan losses. Through such processes loans are categorized into groups to reflect the probability of default, whereby the MHFG Group’s management assesses the ability of borrowers to service their debt, taking into consideration current financial information, ability to generate cash, historical payment experience, analysis of relevant industry segments and current trends. In determining the appropriate level of the allowance, the MHFG Group evaluates the probable loss by category of loan based on its risk type and characteristics.
	The allowance for loan losses is determined in accordance with ASC 310 and ASC 450, “Contingencies” (“ASC 450”). The MHFG Group measures the impairment of a loan when it is probable that the Group will be unable to collect all amounts due according to the contractual terms of the loan agreement, based on (1) the present value of expected future cash flows, after considering the restructuring effect and subsequent payment default with respect to TDRs, discounted at the loan’s initial effective interest rate, (2) the loan’s observable market price, or (3) the fair value of the collateral if the loan is collateral dependent. The collateral that the Group obtains for loans consists primarily of real estate or listed securities. In obtaining the collateral, the Group evaluates the fair value of the collateral and its legal enforceability. The Group also conducts subsequent re-evaluations at least once a year. As it pertains to real estate, valuation is generally conducted by an appraising subsidiary which is independent from the Group’s loan origination sections by using generally accepted valuation techniques such as (1) the replacement cost approach, (2) the sales comparison approach or (3) the income approach. In the case of large real estate collateral, the Group generally retains third-party appraisers to conduct the valuation. As to listed securities, observable market prices are used for valuation.
	The formula allowance is applied to groups of small balance, homogeneous loans that are collectively evaluated for impairment and for non-homogeneous loans that have not been identified as impaired. The evaluation of inherent loss in respect of these loans involves a high degree of uncertainty, subjectivity and judgment because probable loan losses are not easily identifiable or measurable. In determining the formula allowance, the MHFG Group relies on a statistical analysis that incorporates loss rates based on its own historical loss experience and third party data such as the number of corporate default cases which is updated once a year. In determining the allowance amount, the Group analyzes (1) the probability of default: (a) through the most recently available data for the past six years, in the case of normal obligors; and (b) through the most recently available data since April 2002, in the case of watch obligors; and (2) the loss given default through the most recently available data for the past six years. As it pertains to TDR loans in the retail portfolio segment, which are subject to collective evaluation for impairment, the restructuring itself, as well as subsequent payment default, if any, are considered in determining obligor ratings.
	The historical loss rate is adjusted, where appropriate, to reflect current factors, such as general economic and business conditions affecting the key lending areas of the MHFG Group, credit quality trends, specific industry conditions within portfolio segments, and recent loss experience in particular segments of the portfolio. The estimation of the formula allowance is back-tested on a periodic basis by comparing the allowance with the actual results subsequent to the balance sheet date.
	Allowance and provision (credit) for losses on off-balance-sheet instruments
	The MHFG Group maintains an allowance for losses on off-balance-sheet credit instruments, such as guarantees, standby letters of credit, commitments to invest in securities and commitments to extend credit, in the same manner as the allowance for loan losses. The allowance is recorded in Other liabilities. Net changes in the allowance for losses on off-balance-sheet instruments are accounted for in the Provision (credit) for losses on off-balance-sheet instruments in the consolidated statements of income.
	Premises and equipment
	Premises and equipment are stated at historical cost, and depreciation and amortization are recorded over the estimated useful lives of the assets, except for leasehold improvements, which are amortized over the shorter of the estimated useful lives of the assets or the lease term. Depreciation and amortization are principally computed in accordance with the straight-line method with respect to buildings and leasehold improvements and in accordance with the declining-balance method with respect to other premises and equipment.
	The useful lives of premises and equipment are as follows:
		Years
	Buildings		3 to 50
	Equipment and furniture		2 to 20
	Leasehold improvements		2 to 50
	Regular repairs and maintenance costs that do not extend the estimated useful life of an asset are charged to expense as incurred. Upon sale or disposition of premises and equipment, the cost and related accumulated depreciation or amortization are removed from the accounts, and any gains or losses on disposal are included in Gains on disposal of premises and equipment or Occupancy expenses.
	Impairment of long-lived assets
	The MHFG Group’s long-lived assets that are held for use are reviewed periodically for events or changes in circumstances that indicate possible impairment. The Group’s impairment review is based on an undiscounted cash flow analysis of a group of assets, combined with associated liabilities, at the lowest level for which identifiable cash flows exist. Impairment occurs when the carrying value of the asset group exceeds the future undiscounted cash flows that the asset group is expected to generate. When impairment is identified, the future cash flows are then discounted to determine the estimated fair value of the asset group and an impairment charge is recorded for the difference between the carrying value and the estimated fair value of the asset group. The long-lived assets to be disposed of by sale are carried at the lower of the carrying amount or fair value, less estimated cost to sell.
	Software
	Internal and external costs incurred in connection with developing and obtaining software for internal use that occur during the application development stage are capitalized. Such costs include salaries and benefits for employees directly involved with and who devote time to the project, to the extent such time is incurred directly on the internal use software project. The capitalization of software ceases when the software project has been substantially completed. The capitalized software is amortized on a straight-line basis over the estimated useful life, generally 5 to 10 years. Internal use software is reviewed for impairment when triggering events occur.
	Goodwill
	Goodwill represents the excess of the total fair value of the acquired company, which consists of the consideration transferred, the fair value of any interest in the acquiree already held by the acquirer and the fair value of any noncontrolling interest in the acquiree over the fair value of net identifiable assets acquired at the date of acquisition in a business combination. The MHFG Group accounts for goodwill in accordance with ASC 350, “Intangibles—Goodwill and Other” (“ASC 350”). Goodwill is recorded at a designated reporting unit level for the purpose of assessing impairment. An impairment loss is recorded to the extent the carrying amount of goodwill exceeds its estimated fair value.
	Intangible assets
Intangible assets having definite useful lives are amortized over their estimated useful lives on either a straight-line basis or the method that reflects the pattern in which the economic benefits of the intangible assets are consumed. Intangible assets acquired by the merger of MHSC and Shinko Securities Co., Ltd. (“Shinko”) consist primarily of customer relationship intangibles, and are amortized over a weighted-average amortization period of 16 years. Intangible assets having indefinite useful lives are not amortized and are subject to impairment tests. An impairment loss is recorded to the extent the carrying amount of indefinite-lived intangible asset exceeds its estimated fair value. For intangible assets subject to amortization, an impairment loss is recorded if the carrying amount is not recoverable and exceeds its estimated fair value.
Pension and other employee benefits
MHFG and certain subsidiaries sponsor severance indemnities and pension plans, which provide defined benefits to retired employees. Periodic expense and accrued liabilities are computed based on the actuarial present value of benefits, net of investment returns expected from plan assets and their fair values at the balance sheet date. Net periodic expense is charged to Salaries and employee benefits.
Stock-based compensation
The compensation cost associated with stock compensation-type stock options is measured at fair value using the Black-Scholes option pricing model.
Long-term debt
Premiums, discounts and issuance costs of long-term debt are amortized based on a method that approximates the interest method over the respective terms of the long-term debt.
Obligations under guarantees
The MHFG Group provides customers with a variety of guarantees and similar arrangements, including standby letters of credit, financial and performance guarantees, credit protections, and liquidity facilities. The MHFG Group recognizes guarantee fee income over the guarantee period. The MHFG Group receives such a guarantee fee at the inception of the guarantee or in installments and, in either case, the present value of the total fees approximates the fair value of the guarantee.
Fair Value Measurements
The MHFG Group carries certain of its financial assets and liabilities at fair value on a recurring basis. These financial assets and liabilities are primarily composed of trading account assets, trading account liabilities and available-for-sale securities. In addition, the Group measures certain financial assets and liabilities, at fair value on a non-recurring basis. Those assets and liabilities primarily include items that are measured at the lower of cost or fair value such as loans held for sale, and items that were initially measured at cost and have been written down to fair value due to impairments, such as loans and other investments.
Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. In accordance with ASC 820, “Fair Value Measurement” (“ASC 820”), the Group classifies its financial assets and liabilities into the fair value hierarchy (Level 1, 2, and 3). See Note 28 “Fair value” for the detailed definition of each level.
When determining fair value, the MHFG Group considers the principal or most advantageous market in which the Group would transact and considers assumptions that market participants would use when pricing the asset or liability. The Group maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. See Note 28 “Fair value” for descriptions of valuation methodologies used for its assets and liabilities by product.
Fees and commissions
Fee revenue is recognized when all of the following criteria have been met: persuasive evidence of an agreement exists, services have been rendered, the price is fixed or determinable, and collectibility is reasonably assured. Fees on securities-related business and fees on funds transfer and collection services are generally recognized as revenue when the related services are performed. Fees on credit-related business, excluding loan origination fees to be deferred and recognized over the loan period as an adjustment of yield, are generally recognized either at one time when the service is rendered or over the related transaction period. Fees and commissions are presented on a gross basis and exclusive of consumption taxes.
Income taxes
Income taxes are accounted for in accordance with ASC 740, “Income Taxes” (“ASC 740”). Deferred income taxes reflect the net tax effects of (1) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the corresponding amounts used for income tax purposes, and (2) operating loss and tax credit carryforwards. A valuation allowance is recorded for any portion of the deferred tax assets unless it is more likely than not that the deferred tax assets will be realized. Deferred income tax benefit or expense is recognized for the changes in the net deferred tax asset or liability between periods.
Earnings per common share
Basic earnings per common share are computed by dividing net income attributable to MHFG common shareholders by the weighted average number of common shares outstanding during the fiscal year. Diluted earnings per common share reflect the possible exercise of all convertible securities, such as convertible preferred stock to the extent they are not anti-dilutive. See Note 18 “Earnings per common share” for the computation of basic and diluted earnings per common share.

Recently_issued_accounting_pro

Recently issued accounting pronouncements	12 Months Ended
	Mar. 31, 2014
Recently issued accounting pronouncements	'
	2. Recently issued accounting pronouncements
	Recently adopted accounting pronouncements
	On July 1, 2009, the ASC was officially launched. The ASC, which reorganized the thousands of U.S. GAAP pronouncements into roughly 90 accounting topics, is the single source of authoritative U.S. GAAP for nongovernmental entities.
	In January 2010, the FASB issued Accounting Standards Update (“ASU”) No.2010-06, “Fair Value Measurements and Disclosures (Topic 820)—Improving Disclosures about Fair Value Measurements” (“ASU No.2010-06”). The ASU provides amendments to ASC 820 that require new disclosures regarding (1) transfers in and out of Levels 1 and 2 and (2) more detailed activity in Level 3. The ASU also provides amendments to ASC 820 that clarify existing disclosures regarding (1) level of disaggregation and (2) inputs and valuation techniques. The ASU is effective for interim and annual reporting periods beginning after December 15, 2009, except for the new disclosures related to the activity in Level 3, which do not become effective until fiscal years beginning after December 15, 2010, and for interim periods within those fiscal years. ASU No.2010-06 is an accounting principle which expands disclosure requirements, and had no impact on the MHFG Group’s consolidated results of operations or financial condition.
	In July 2010, the FASB issued ASU No.2010-20, “Receivables (Topic 310)—Disclosures about the Credit Quality of Financing Receivables and the Allowance for Credit Losses” (“ASU No.2010-20”). The ASU requires disclosures that facilitate financial statement users’ evaluation of (1) the nature of credit risk inherent in the entity’s portfolio of financing receivables, (2) how that risk is analyzed and assessed in arriving at the allowance for credit losses and (3) the changes and reasons for those changes in the allowance for credit losses. The new disclosures required include (1) aging of past due receivables, (2) credit quality indicators, and (3) modifications of financing receivables. It is also required that certain existing disclosures should be provided on a disaggregated basis. The disclosures as of the end of a reporting period are effective for interim and annual reporting periods ending on or after December 15, 2010, whereas the disclosures about activity that occurs during a reporting period are effective for interim and annual reporting periods beginning on or after December 15, 2010. In January 2011, the FASB issued ASU No.2011-01, “Receivables (Topic310)—Deferral of the Effective Date of Disclosures about Troubled Debt Restructurings in Update No.2010-20” (“ASU No.2011-01”) to delay the effective date of the disclosures about troubled debt restructurings for public entities, and in April 2011, it was provided that such disclosure requirements would be effective for interim and annual periods beginning on or after June 15, 2011 in ASU No.2011-02, “Receivables (Topic310)—A Creditor’s Determination of Whether a Restructuring Is a Troubled Debt Restructuring” (“ASU No.2011-02”). ASU No.2011-02 also clarifies the guidance on a creditor’s evaluation for troubled debt restructurings of whether it has granted a concession and whether a debtor is experiencing financial difficulties. ASU No.2010-20 is an accounting principle which expands disclosure requirements, and had no impact on the MHFG Group’s consolidated results of operations or financial condition.
	In December 2010, the FASB issued ASU No.2010-28, “Intangibles—Goodwill and Other (Topic 350)—When to Perform Step 2 of the Goodwill Impairment Test for Reporting Units with Zero or Negative Carrying Amounts” (“ASU No.2010-28”). The ASU requires that Step 2 of the impairment test should be performed in circumstances where the carrying amount of a reporting unit is zero or negative and there are qualitative factors that indicate it is more likely than not that a goodwill impairment exists. The ASU is effective for fiscal years, and interim periods within those years, beginning after December 15, 2010. The adoption of ASU No.2010-28 did not have a material impact on the MHFG Group’s consolidated results of operations or financial condition.
	In December 2010, the FASB issued ASU No.2010-29, “Business Combinations (Topic 805)—Disclosure of Supplementary Pro Forma Information for Business Combinations” (“ASU No.2010-29”). The ASU clarifies that, if a reporting entity presents comparative financial statements, the pro forma revenue and earnings of the combined entity should be reported as though the business combinations that occurred during the current year had occurred as of the beginning of the comparable prior annual reporting period only. The ASU is effective prospectively for business combinations for which the acquisition date is on or after the beginning of the first annual reporting period beginning on or after December 15, 2010. ASU No.2010-29 is an accounting principle which clarifies disclosure requirements, and had no impact on the MHFG Group’s consolidated results of operations or financial condition.
	In April 2011, the FASB issued ASU No.2011-03, “Transfers and Servicing (Topic 860)—Reconsideration of Effective Control for Repurchase Agreements” (“ASU No.2011-03”). The ASU amends the conditions to determine whether a transferor in repurchase agreements (repos) and other similar agreements maintains effective control over the financial assets transferred by removing from the assessment of effective control (1) the criterion requiring the transferor to have the ability to repurchase or redeem the financial assets on substantially the agreed terms, even in the event of default by the transferee, and (2) the collateral maintenance implementation guidance related to that criterion. The ASU is effective for the first interim or annual period beginning on or after December 15, 2011, and should be applied prospectively to transactions or modifications of existing transactions that occur on or after the effective date. The adoption of ASU No.2011-03 did not have a material impact on the MHFG Group’s consolidated results of operations or financial condition.
	In May 2011, the FASB issued ASU No. 2011-04, “Fair Value Measurement (Topic 820)—Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs” (“ASU No.2011-04”) in order to improve comparability of fair value measurements presented and disclosed in financial statements prepared in accordance with U.S. GAAP and International Financial Reporting Standards (“IFRS”). The amendments in ASU No. 2011-04 change the wording to describe the requirements in U.S. GAAP for measuring fair value and for disclosing information about fair value measurements to align with IFRS. The amendments also clarify the existing fair value measurement and disclosure requirements, which include (1) application of the highest and best use and valuation premise concepts, (2) measuring the fair value of an instrument classified in a reporting entity’s shareholders’ equity and (3) disclosing quantitative information about the unobservable inputs used for Level 3 items. The amendments also change a particular principle or requirement for measuring fair value or for disclosing information about fair value measurements, which include (1) measuring the fair value of financial instruments that are managed within a portfolio, (2) application of premiums and discounts in a fair value measurement and (3) additional disclosures about fair value measurements. The ASU is effective for interim and annual periods beginning after December 15, 2011. The adoption of ASU No.2011-04 did not have a material impact on the MHFG Group’s consolidated results of operations or financial condition.
	In June 2011, the FASB issued ASU No.2011-05, “Comprehensive Income (Topic 220)—Presentation of Comprehensive Income” (“ASU No.2011-05”). The ASU eliminates the option to present components of other comprehensive income as part of the statement of changes in stockholders’ equity, and requires that all nonowner changes in stockholders’ equity be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements. The ASU also requires reclassification adjustments from other comprehensive income to net income be presented on the face of financial statements. The ASU is effective for fiscal years, and interim periods within those years, beginning after December 15, 2011, and should be applied retrospectively. In December 2011, the FASB issued ASU No.2011-12, “Comprehensive Income (Topic 220)—Deferral of the Effective Date for Amendments to the Presentation of Reclassifications of Items Out of Accumulated Other Comprehensive Income in Accounting Standards Update No.2011-05” (“ASU No.2011-12”) to indefinitely defer only those changes in ASU No.2011-05 that relate to the presentation of reclassification adjustments. All other requirements in ASU No.2011-05 are not affected, and entities should continue to report reclassifications out of accumulated other comprehensive income consistent with the presentation requirements in effect before ASU No.2011-05. ASU No.2011-05 is an accounting principle which alters disclosure requirements, and had no impact on the MHFG Group’s consolidated results of operations or financial condition.
	In September 2011, the FASB issued ASU No.2011-08, “Intangibles—Goodwill and Other (Topic 350)—Testing Goodwill for Impairment” (“ASU No.2011-08”). The ASU permits an entity the option to first assess qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount as a basis for determining whether it is necessary to perform the two-step goodwill impairment test. Under this ASU, an entity is not required to calculate the fair value of a reporting unit unless the entity determines that it is more likely than not that its fair value is less than its carrying amount. The ASU is effective for annual and interim goodwill impairment tests performed for fiscal years beginning after December 15, 2011. The adoption of ASU No.2011-08 did not have a material impact on the MHFG Group’s consolidated results of operations or financial condition.
	In December 2011, the FASB issued ASU No.2011-10, “Property, Plant, and Equipment (Topic 360)—Derecognition of in Substance Real Estate—a Scope Clarification” (“ASU No.2011-10”). The ASU clarifies that, even when a reporting entity ceases to have a controlling financial interest in a subsidiary that is in substance real estate as a result of default on the subsidiary’s nonrecourse debt, the reporting entity would continue to include the real estate, debt, and the results of the subsidiary’s operations in its consolidated financial statements until legal title to the real estate is transferred to legally satisfy the debt. The ASU is effective for fiscal years and interim periods within those years, beginning on or after June 15, 2012. The adoption of ASU No.2011-10 did not have a material impact on the MHFG Group’s consolidated results of operations or financial condition.
	In December 2011, the FASB issued ASU No.2011-11, “Balance Sheet (Topic 210)—Disclosures about Offsetting Assets and Liabilities” (“ASU No.2011-11”). The ASU enhances disclosures by requiring improved information about financial instruments and derivative instruments that are either (1) offset on the statement of financial position or (2) subject to an enforceable master netting arrangement or similar agreement, irrespective of whether they are offset on the statement of financial position. Under the ASU, entities are required to provide both net and gross information for these financial instruments and derivative instruments in order to enhance comparability between those entities that prepare their financial statements on the basis of U.S. GAAP and those entities that prepare their financial statements on the basis of IFRS. The ASU is effective for annual reporting periods beginning on or after January 1, 2013 and interim periods within those annual periods. An entity should provide the disclosures required retrospectively for all comparative periods presented. In January 2013, the FASB issued ASU No.2013-01, “Balance Sheet (Topic 210)—Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities” (“ASU No.2013-01”). ASU No.2013-01 clarifies that the scope of ASU No.2011-11 applies to derivatives including bifurcated embedded derivatives, repurchase agreements and reverse repurchase agreements, and securities borrowing and securities lending transactions. ASU No.2011-11 is an accounting principle which expands disclosure requirements, and had no impact on the MHFG Group’s consolidated results of operations or financial condition.
	In July 2012, the FASB issued ASU No.2012-02, “Intangibles—Goodwill and Other (Topic 350)—Testing Indefinite-Lived Intangible Assets for Impairment” (“ASU No.2012-02”). The ASU permits an entity first to assess qualitative factors to determine whether it is more likely than not that an indefinite-lived intangible asset is impaired as a basis for determining whether it is necessary to perform the quantitative impairment test. Under this ASU, an entity has an option not to calculate annually the fair value of an indefinite-lived intangible asset if the entity determines that it is not more likely than not that its fair value is less than its carrying amount. The ASU is effective for annual and interim impairment tests performed for fiscal years beginning after September 15, 2012. The adoption of ASU No.2012-02 did not have a material impact on the MHFG Group’s consolidated results of operations or financial condition.
	In February 2013, the FASB issued ASU No.2013-02, “Comprehensive Income (Topic 220)—Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income” (“ASU No.2013-02”). The ASU requires an entity to present, either on the face of the statement where net income is presented or in the notes, significant amounts reclassified out of accumulated other comprehensive income by the respective line items of net income. The ASU also requires an entity to provide information about the amounts reclassified out of accumulated other comprehensive income by component. The ASU is effective for reporting periods beginning after December 15, 2012. ASU No.2013-02 is an accounting principle which expands disclosure requirements, and had no impact on the MHFG Group’s consolidated results of operations or financial condition.
	Accounting pronouncements issued but not yet effective
	In June 2013, the FASB issued ASU No.2013-08, “Financial Services—Investment Companies (Topic 946)—Amendments to the Scope, Measurement, and Disclosure Requirements” (“ASU No.2013-08”). The ASU changes the approach to the investment company assessment and requires an investment company to measure noncontrolling ownership interests in other investment companies at fair value. The ASU also requires additional disclosures of (a) the fact that the entity is an investment company and is applying the guidance in ASC 946, “Financial Services—Investment Companies”, (b) information about changes, if any, in an entity’s status as an investment company, and (c) information about financial support provided or contractually required to be provided by an investment company to any of its investees. The ASU is effective for an entity’s interim and annual reporting periods in fiscal years that begin after December 15, 2013. Early adoption is prohibited. The MHFG Group does not expect that the adoption of ASU No.2013-08 will have a material impact on its consolidated results of operations and financial condition.
	In May 2014, the FASB issued ASU No.2014-09, “Revenue from Contracts with Customers (Topic 606)” (“ASU No.2014-09”). The ASU provides a comprehensive guidance of revenue recognition, in convergence with IFRS, to improve financial reporting in U.S. GAAP by replacing the current complex guidance for recognizing revenue. The core principle of this ASU is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve that core principle, an entity should apply the following five steps: (1) identify the contract(s) with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract, and (5) recognize revenue when ( or as) the entity satisfies a performance obligation. In order to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers, an entity should disclose the following quantitative and qualitative information: (1) contracts with customers—including revenue and impairments recognized, disaggregation of revenue, and information about contract balances and performance obligations, (2) significant judgments and changes in judgments—determining the timing of satisfaction of performance obligations, and determining the transaction price and amounts allocated to performance obligations, and (3) assets recognized from the costs to obtain or fulfill a contract. The ASU is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. Early application is not permitted. The MHFG Group is currently evaluating the potential impact that the adoption of ASU No.2014-09 will have on its consolidated results of operations and financial condition.
	In June 2014, the FASB issued ASU No.2014-11, “Transfers and Servicing (Topic 860)—Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures” (“ASU No.2014-11”). The ASU changes the accounting for repurchase-to-maturity transactions to secured borrowing accounting. For repurchase financing arrangements, the ASU requires separate accounting for a transfer of a financial asset executed contemporaneously with a repurchase agreement with the same counterparty, which will result in secured borrowing accounting for the repurchase agreement. The ASU requires disclosures for certain transactions comprising (1) a transfer of a financial asset accounted for as a sale and (2) an agreement with the same transferee entered into in contemplation of the initial transfer that results in the transferor retaining substantially all of the exposure to the economic return on the transferred financial asset throughout the term of the transaction. The ASU also requires an entity to disclose certain information, including risks related to collateral pledged, for repurchase agreements, securities lending transactions, and repurchase-to-maturity transactions that are accounted for as secured borrowings. The ASU is effective for the first interim or annual period beginning after December 15, 2014, except for interim disclosure requirements related to secured borrowings, which are effective for interim periods beginning after March 15, 2015. Earlier application is prohibited. The MHFG Group does not expect that the adoption of ASU No.2014-11 will have a material impact on its consolidated results of operations and financial condition.

Investments

Investments	12 Months Ended
	Mar. 31, 2014
Investments	'
	3. Investments
	The amortized cost, gross unrealized gains and losses, and fair value of available-for-sale and held-to-maturity securities at March 31, 2013 and 2014 are as follows:
			Amortized cost		Gross unrealized		Gross unrealized		Fair value
					gains		losses
			(in millions of yen)
	2013
	Available-for-sale securities:
	Debt securities:
	Japanese government bonds			30,709,499		79,378		5,677		30,783,200
	Japanese local government bonds			239,695		4,109		47		243,757
	U.S. Treasury bonds and federal agency securities			177,438		623		36		178,025
	Other foreign government bonds			596,305		1,914		94		598,125
	Agency mortgage-backed securities (1)			986,646		20,496		1,429		1,005,713
	Residential mortgage-backed securities			430,325		13,889		2,131		442,083
	Commercial mortgage-backed securities			246,169		7,487		3,528		250,128
	Japanese corporate bonds and other debt securities (2)			2,197,270		22,582		5,288		2,214,564
	Foreign corporate bonds and other debt securities (3)			542,958		17,768		1,803		558,923
	Equity securities (marketable)			1,699,475		1,440,102		144		3,139,433
	Total			37,825,780		1,608,348		20,177		39,413,951
	Held-to-maturity securities:
	Debt securities:
	Japanese government bonds			3,000,403		20,023		82		3,020,344
	Total			3,000,403		20,023		82		3,020,344
	2014
	Available-for-sale securities:
	Debt securities:
	Japanese government bonds			22,039,640		20,063		3,727		22,055,976
	Japanese local government bonds			241,985		2,783		106		244,662
	U.S. Treasury bonds and federal agency securities			158,344		434		4,297		154,481
	Other foreign government bonds			719,281		2,356		455		721,182
	Agency mortgage-backed securities (1)			955,291		13,288		7,705		960,874
	Residential mortgage-backed securities			318,955		14,757		1,707		332,005
	Commercial mortgage-backed securities			159,289		3,032		1,417		160,904
	Japanese corporate bonds and other debt securities (2)			2,015,045		16,316		3,284		2,028,077
	Foreign corporate bonds and other debt securities (3)			559,947		10,755		2,193		568,509
	Equity securities (marketable)			1,667,669		1,761,025		6,603		3,422,091
	Total			28,835,446		1,844,809		31,494		30,648,761
	Held-to-maturity securities:
	Debt securities:
	Japanese government bonds			4,040,083		17,954		220		4,057,817
	Total			4,040,083		17,954		220		4,057,817
	Notes	:
	-1	Agency mortgage-backed securities presented in the above table consist of U.S. agency securities and Japanese agency securities, of which the fair values were ¥143,954 million and ¥861,759 million, respectively, at March 31, 2013, and ¥105,553 million and ¥855,321 million, respectively, at March 31, 2014. U.S. agency securities primarily consist of Government National Mortgage Association or Ginnie Mae securities, which are guaranteed by the United States government. All Japanese agency securities are mortgage-backed securities issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise.
	-2	Other debt securities presented in the above table primarily consist of certificates of deposit (“CDs”) and asset-backed securities (“ABS”), of which the total fair values were ¥185,497 million at March 31,2013, and ¥214,488 million at March 31, 2014.
	-3	Other debt securities presented in the above table primarily consist of CDs, ABS, and collateral loan obligations (“CLO”), of which the total fair values were ¥243,633 million at March 31,2013, and ¥178,055 million at March 31, 2014.
	The amortized cost and fair value of available-for-sale and held-to-maturity debt securities at March 31, 2014 by contractual maturity are shown in the table below. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalties. Securities not due at a single maturity date and securities embedded with call or prepayment options, such as mortgage-backed securities, are included in the table below based on their contractual maturities.
	Amortized cost		Due in one		Due after one		Due after five		Due after		Total
			year or less		year through		years through		ten years
					five years		ten years
			(in millions of yen)
	Available-for-sale securities:
	Debt securities:
	Japanese government bonds			5,926,354		13,876,023		2,237,263		—		22,039,640
	Japanese local government bonds			30,346		130,751		80,108		780		241,985
	U.S. Treasury bonds and federal agency securities			43,475		75,005		39,864		—		158,344
	Other foreign government bonds			507,140		211,949		—		192		719,281
	Agency mortgage-backed securities			—		—		—		955,291		955,291
	Residential mortgage-backed securities			—		—		—		318,955		318,955
	Commercial mortgage-backed securities			4,085		123,455		31,749		—		159,289
	Japanese corporate bonds and other debt securities			369,682		1,131,664		326,861		186,838		2,015,045
	Foreign corporate bonds and other debt securities			221,916		251,536		83,865		2,630		559,947
	Total			7,102,998		15,800,383		2,799,710		1,464,686		27,167,777
	Held-to-maturity securities:
Debt securities:
Japanese government bonds			600,047		3,080,346		359,690		—		4,040,083
Total			600,047		3,080,346		359,690		—		4,040,083
Fair value		Due in one		Due after one		Due after five		Due after		Total
		year or less		year through		years through		ten years
				five years		ten years
		(in millions of yen)
Available-for-sale securities:
Debt securities:
Japanese government bonds			5,926,642		13,882,371		2,246,963		—		22,055,976
Japanese local government bonds			30,384		131,438		81,952		888		244,662
U.S. Treasury bonds and federal agency securities			43,907		72,142		38,432		—		154,481
Other foreign government bonds			507,577		213,355		—		250		721,182
Agency mortgage-backed securities			—		—		—		960,874		960,874
Residential mortgage-backed securities			—		—		—		332,005		332,005
Commercial mortgage-backed securities			4,087		124,981		31,836		—		160,904
Japanese corporate bonds and other debt securities			370,157		1,137,145		329,033		191,742		2,028,077
Foreign corporate bonds and other debt securities			222,527		253,142		89,625		3,215		568,509
Total			7,105,281		15,814,574		2,817,841		1,488,974		27,226,670
Held-to-maturity securities:
Debt securities:
Japanese government bonds			601,750		3,091,769		364,298		—		4,057,817
Total			601,750		3,091,769		364,298		—		4,057,817
In accordance with ASC 320, “Investments—Debt and Equity Securities” (“ASC 320”), for debt securities, if an entity has the intent to sell a debt security or more likely than not will be required to sell a debt security before recovery of its amortized cost basis, the full amount of an other-than-temporary impairment loss shall be recognized immediately through earnings. Other than either case described above, an entity must evaluate expected cash flows to be received and determine if a credit loss exists, and if so, the amount of an other-than-temporary impairment related to the credit loss shall be recognized in earnings, while the remaining decline in fair value shall be recognized in other comprehensive income, net of applicable taxes. For equity securities, if an equity security is deemed other-than-temporarily impaired, it shall be written down to fair value, with the full decline recognized in earnings.
The MHFG Group performs periodic reviews to identify impaired securities. Impairment is evaluated considering the length of time and extent to which the fair value has been below cost, the financial condition and near-term prospects of the issuer, as well as the MHFG Group’s ability and intent to hold the investments for a reasonable period of time until a forecasted recovery of fair value or maturity.
For the fiscal years ended March 31, 2012, 2013 and 2014, the MHFG Group recognized in earnings the other-than-temporary impairment on available-for-sale securities of ¥117,029 million, ¥76,393 million and ¥5,344 million, respectively, of which ¥7,238 million, ¥4,085 million and ¥1,151 million, respectively, were on debt securities and ¥109,791 million, ¥72,308 million and ¥4,193 million, respectively, were on equity securities. No impairment losses were recognized on held-to-maturity securities for the periods.
The other-than-temporary impairment losses for debt securities were mainly attributable to the decline in the fair value of commercial mortgage-backed securities (“CMBS”) that the MHFG Group had the intent to sell. In accordance with ASC 320-10-35-33A and ASC 320-10-35-34B, the other-than-temporary impairment of these securities was recognized in earnings. There has never been any instance related to credit losses recognized in earnings on debt securities where a portion of an other-than-temporary impairment was recognized in other comprehensive income.
The other-than-temporary impairment losses for equity securities were mainly attributable to the decline in the fair value of Japanese equity securities. Certain equity securities were determined not to be other-than-temporarily impaired based on the evaluation of the following factors: (1) the severity and duration of the impairments, (2) the financial condition and near-term prospects of the issuers, and (3) the MHFG Group’s ability and intent to hold those investments for a reasonable period of time sufficient for a forecasted recovery of fair value.
The following tables show the gross unrealized losses and fair value of available-for-sale and held-to-maturity securities, aggregated by the length of time that individual securities have been in a continuous unrealized loss position, at March 31, 2013 and 2014:
		Less than 12 months				12 months or more				Total
		Fair		Gross		Fair		Gross		Fair		Gross
		value		unrealized		value		unrealized		value		unrealized
				losses				losses				losses
		(in millions of yen)
2013
Available-for-sale securities:
Debt securities:
Japanese government bonds			5,059,495		1,520		406,684		4,157		5,466,179		5,677
Japanese local government bonds			27,243		47		—		—		27,243		47
U.S. Treasury bonds and federal agency securities			69,168		36		—		—		69,168		36
Other foreign government bonds			207,942		94		—		—		207,942		94
Agency mortgage-backed securities (1)			90,832		1,429		—		—		90,832		1,429
Residential mortgage-backed securities			12,778		9		122,363		2,122		135,141		2,131
Commercial mortgage-backed securities			7,159		111		122,588		3,417		129,747		3,528
Japanese corporate bonds and other debt securities			88,146		333		222,516		4,955		310,662		5,288
Foreign corporate bonds and other debt securities			54,599		114		65,417		1,689		120,016		1,803
Equity securities (marketable)			8,488		128		699		16		9,187		144
Total			5,625,850		3,821		940,267		16,356		6,566,117		20,177
Held-to-maturity securities:
Debt securities:
Japanese government bonds			199,730		82		—		—		199,730		82
Total			199,730		82		—		—		199,730		82
2014
Available-for-sale securities:
Debt securities:
Japanese government bonds			10,526,182		2,871		880,520		856		11,406,702		3,727
Japanese local government bonds			48,471		90		12,730		16		61,201		106
U.S. Treasury bonds and federal agency securities			66,865		2,865		38,432		1,432		105,297		4,297
Other foreign government bonds			203,026		275		7,654		180		210,680		455
Agency mortgage-backed securities (2)			102,904		2,348		76,369		5,357		179,273		7,705
Residential mortgage-backed securities			9,771		137		78,938		1,570		88,709		1,707
Commercial mortgage-backed securities			11,133		117		43,170		1,300		54,303		1,417
Japanese corporate bonds and other debt securities			130,020		359		60,230		2,925		190,250		3,284
Foreign corporate bonds and other debt securities			122,563		1,846		33,960		347		156,523		2,193
Equity securities (marketable)			132,590		6,603		10		—		132,600		6,603
Total			11,353,525		17,511		1,232,013		13,983		12,585,538		31,494
Held-to-maturity securities:
Debt securities:
Japanese government bonds			9,962		40		199,670		180		209,632		220
Total			9,962		40		199,670		180		209,632		220
Notes	:
-1	Agency mortgage-backed securities presented in the above table represent U.S. agency securities. U.S. agency securities primarily consist of Government National Mortgage Association or Ginnie Mae securities, which are guaranteed by the United States government.
-2	Agency mortgage-backed securities presented in the above table consist of U.S. agency securities and Japanese agency securities, of which the fair values were ¥105,208 million and ¥74,065 million, respectively, at March 31, 2014. All Japanese agency securities are mortgage-backed securities issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise.
The unrealized losses on investments in a continuous loss position for 12 months or more at March 31, 2014 were attributed mainly to Agency mortgage-backed securities and Japanese corporate bonds and other debt securities. The MHFG Group did not intend to sell those securities and it was not more likely than not that the Group would be required to sell them before recovery of their amortized cost basis. Those securities were not considered other-than-temporarily impaired. As to CMBS and Japanese corporate bonds and other debt securities with similar credit risks as the other-than-temporarily impaired securities, and Agency mortgage-backed securities and Residential mortgage-backed securities (“RMBS”), the Group determined that it was expected to recover their entire amortized cost basis, after considering various factors such as the extent to which their fair values were below their amortized costs, the external and/or internal ratings and the present values of cash flows expected to be collected. As to Japanese government bonds, since the unrealized losses had not resulted from credit deterioration, but primarily from changes in interest rates, their entire amortized cost basis was expected to be collected.
For the fiscal years ended March 31, 2012, 2013 and 2014, the gross realized gains on sales of available-for-sale securities were ¥100,371 million, ¥193,298 million and ¥231,955 million, respectively, and the gross realized losses on those sales were ¥28,840 million, ¥21,422 million and ¥29,387 million, respectively.
Other investments
The following table summarizes the composition of Other investments:
		2013		2014
		(in millions of yen)
Equity method investments			225,696		196,015
Investments held by consolidated investment companies			75,780		70,599
Other equity interests			536,659		526,075
Total			838,135		792,689
Equity method investments
Investments in investees over which the MHFG Group has the ability to exert significant influence are accounted for using the equity method of accounting. For the fiscal years ended March 31, 2012, 2013 and 2014, the earnings (losses) from equity method investments were ¥10,807 million, (¥2,192) million and ¥27,975 million, respectively. Such investments included marketable equity securities carried at ¥68,289 million and ¥78,458 million, at March 31, 2013 and 2014, respectively. The aggregate market values of these marketable equity securities were ¥111,543 million and ¥96,471 million, respectively.
The MHFG Group’s proportionate share of the total outstanding common shares in Orient Corporation (“Orico”) as of March 31, 2014 was 22.2% and the Group and a certain third party still hold convertible preferred shares of Orico, and if fully converted, the Group’s proportionate share of the total outstanding common shares in Orico would increase to 58.0%.
Investments held by consolidated investment companies
The MHFG Group consolidates certain investment companies over which it has control through either ownership or other means. Investment companies are subject to specialized industry accounting which requires investments to be carried at fair value, with changes in fair value recorded in earnings. The MHFG Group maintains this specialized industry accounting for investments held by consolidated investment companies, which consist of marketable and non-marketable investments.
Other equity interests
Other equity interests consist primarily of non-marketable equity securities outside the scope of ASC 320, of which the fair values are not readily determinable. The MHFG Group has neither significant influence nor control over the investees. Each of these securities is stated at acquisition cost, with an other-than-temporary impairment, if any, included in earnings. The MHFG Group monitors the status of each investee, including its credit rating, to determine whether impairment losses should be recognized.

Loans

Loans	12 Months Ended
	Mar. 31, 2014
Loans	'
	4. Loans
	The table below presents loans outstanding by domicile and industry of borrower at March 31, 2013 and 2014:
			2013			2014
			(in millions of yen)
	Domestic:
	Manufacturing			8,078,871			8,025,932
	Construction and real estate			7,477,853			7,204,594
	Services			3,972,011			3,956,742
	Wholesale and retail			5,355,974			5,350,707
	Transportation and communications			3,147,106			3,247,394
	Banks and other financial institutions			3,142,998			3,460,147
	Government and public institutions			6,907,426			6,734,451
	Other industries (Note)			4,521,994			4,983,821
	Individuals:
	Mortgage loans			11,234,561			11,187,206
	Other			741,519			787,313
	Total domestic			54,580,313			54,938,307
	Foreign:
	Commercial and industrial			10,481,071			12,937,005
	Banks and other financial institutions			4,088,651			4,610,141
	Government and public institutions			595,911			883,004
	Other (Note)			199,518			255,083
	Total foreign			15,365,151			18,685,233
	Total			69,945,464			73,623,540
	Less: Unearned income and deferred loan fees—net			111,981			138,586
	Total loans before allowance for loan losses			69,833,483			73,484,954
	Note:	Other industries of domestic and Other of foreign include trade receivables and lease receivables of consolidated VIEs.
	Net losses on sales of loans were ¥4,576 million, ¥853 million and ¥2,041 million, of which valuation losses related to loans held for sale accounted for at the lower of cost or fair value were ¥3,435 million, ¥54 million and ¥1,510 million for the fiscal years ended March 31, 2012, 2013 and 2014, respectively.
	Credit quality information
	In accordance with the MHFG Group’s credit risk management policies, the Group uses an internal rating system that consists of credit ratings and pool allocations as the basis of its risk management infrastructure. Credit ratings consist of obligor ratings which represent the level of credit risk of the obligor, and transaction ratings which represent the ultimate possibility of incurring losses on individual loan by taking into consideration various factors such as collateral or guarantees involved. In principle, obligor ratings are applied to all obligors except those to which pool allocations are applied, and are subject to regular review at least once a year as well as special review which is required whenever the obligor’s credit standing changes. Pool allocations are applied to small balance loans. The Group pools loans with similar risk characteristics, and the risk is assessed and managed according to such pools. The Group generally reviews the appropriateness and effectiveness of the approach to obligor ratings and pool allocations once a year in accordance with predetermined procedures.
	The table below presents the MHFG Group’s definition of obligor ratings used by MHBK and MHTB:
	Obligor category		Obligor rating		Definition
	Normal		A		Obligors whose certainty of debt fulfillment is very high, hence their level of credit risk is very low.
			B		Obligors whose certainty of debt fulfillment poses no problems for the foreseeable future, and their level of credit risk is low.
			C		Obligors whose certainty of debt fulfillment and their level of credit risk pose no problems for the foreseeable future.
			D		Obligors whose current certainty of debt fulfillment poses no problems, however, their resistance to future environmental changes is low.
	Watch		E1		Obligors that require observation going forward because of either minor concerns regarding their financial position, or somewhat weak or unstable business conditions.
			E2		Obligors that require special observation going forward because of problems with their borrowings such as reduced or suspended interest payments, problems with debt fulfillment such as failure of principal or interest payments, or problems with their financial position as a result of their weak or unstable business condition.
	Intensive control		F		Obligors that are not yet bankrupt but are in financial difficulties and are deemed likely to become bankrupt in the future because of insufficient progress in implementing their management improvement plans or other measures (including obligors that are receiving ongoing support from financial institutions).
	Substantially bankrupt		G		Obligors that have not yet become legally or formally bankrupt but are substantially insolvent because they are in serious financial difficulties and are deemed to be incapable of being restructured.
	Bankrupt		H		Obligors that have become legally or formally bankrupt.
	The table below presents credit quality information of loans based on the MHFG Group’s internal rating system at March 31, 2013 and 2014:
			Normal obligors									Watch obligors excluding						Impaired		Total
												special attention obligors (1)						loans
			A-B			C-D		Retail (2)		Other (3)		E1-E2		Retail (2)		Other (3)
			(in millions of yen)
	2013
	Domestic:
	Manufacturing			4,171,212			2,615,406		119,183		307,946		498,638		22,569		8,013		335,904		8,078,871
	Construction and real estate			2,524,644			3,486,850		659,844		148,893		387,254		20,671		664		249,033		7,477,853
	Services			1,736,931			1,734,482		219,089		4,035		160,754		26,621		—		90,099		3,972,011
	Wholesale and retail			1,853,573			2,699,053		261,322		83,065		236,545		49,710		11		172,695		5,355,974
	Transportation and communications			2,236,404			685,237		94,233		350		59,573		12,274		—		59,035		3,147,106
	Banks and other financial institutions			2,246,804			666,197		2,172		5,311		208,510		221		—		13,783		3,142,998
	Government and public institutions			6,797,133			11,729		—		98,564		—		—		—		—		6,907,426
	Other industries			1,620,061			743,214		3,341		2,058,974		13,044		448		77,548		5,364		4,521,994
	Individuals			—			191,360		11,219,209		170,768		33,618		121,468		4,032		235,625		11,976,080
	Total domestic			23,186,762			12,833,528		12,578,393		2,877,906		1,597,936		253,982		90,268		1,161,538		54,580,313
	Foreign:
	Total foreign			8,293,654			3,650,488		4,881		2,021,284		980,343		137		111,684		302,680		15,365,151
	Total			31,480,416			16,484,016		12,583,274		4,899,190		2,578,279		254,119		201,952		1,464,218		69,945,464
	2014
	Domestic:
Manufacturing			4,248,490			2,467,326		109,258		310,703		636,348		21,117		3,820		228,870		8,025,932
Construction and real estate			2,890,563			3,066,852		623,385		161,177		303,746		20,577		381		137,913		7,204,594
Services			1,946,764			1,558,609		205,939		6,998		135,030		24,958		—		78,444		3,956,742
Wholesale and retail			2,029,723			2,632,048		249,304		63,116		178,520		42,086		10		155,900		5,350,707
Transportation and communications			2,388,541			658,680		88,911		1,348		50,667		11,159		—		48,088		3,247,394
Banks and other financial institutions			2,602,545			664,843		2,030		4,780		174,328		165		—		11,456		3,460,147
Government and public institutions			6,678,104			8,347		—		48,000		—		—		—		—		6,734,451
Other industries			1,907,714			754,137		3,383		2,240,879		7,804		401		68,642		861		4,983,821
Individuals			—			197,725		11,266,620		169,655		40,606		101,718		2,823		195,372		11,974,519
Total domestic			24,692,444			12,008,567		12,548,830		3,006,656		1,527,049		222,181		75,676		856,904		54,938,307
Foreign:
Total foreign			10,600,531			4,349,587		6,621		2,782,476		513,610		14		144,238		288,156		18,685,233
Total			35,292,975			16,358,154		12,555,451		5,789,132		2,040,659		222,195		219,914		1,145,060		73,623,540
Notes:
-1	Special attention obligors are watch obligors with debt in TDR or 90 days or more delinquent debt. Loans to such obligors are considered impaired.
-2	Amounts represent small balance, homogeneous loans which are subject to pool allocations.
-3	The former MHBK and the former Mizuho Corporate Bank, Ltd. (“MHCB”) merged on July 1, 2013 and the former MHCB, the surviving company, changed its trade name to MHBK. As of March 31, 2013, non-impaired loans held by subsidiaries other than the former MHBK, the former MHCB and MHTB constitute Other, since their portfolio segments are not identical to those used by the former MHBK, the former MHCB and MHTB. As of March 31, 2014, non-impaired loans held by subsidiaries other than MHBK and MHTB constitute Other, since their portfolio segments are not identical to those used by MHBK and MHTB.
Impaired loans
The MHFG Group considers loans to be impaired when it is probable that the Group will be unable to collect all the scheduled payments of principal and interest when due according to the contractual terms of the loan. The Group classifies loans to special attention, intensive control, substantially bankrupt and bankrupt obligors as impaired loans, and all of the Group’s impaired loans are designated as nonaccrual loans. The Group does not have any loans to borrowers that cause management to have serious doubts as to the ability of such borrowers to comply with the present loan repayment terms for the periods presented other than those already designated as impaired loans. The table below presents impaired loans information at March 31, 2013 and 2014.
		Recorded investment (1)							Unpaid		Related		Average		Interest
									principal		allowance (3)		recorded		income
		Requiring an			Not		Total		balance				investment		recognized (4)
		allowance for			requiring an
		loan losses			allowance
					for loan
					losses (2)
		(in millions of yen)
2013
Domestic:
Manufacturing			325,727			10,177		335,904		365,049		118,475		299,978		5,297
Construction and real estate			189,060			59,973		249,033		269,770		46,574		227,920		2,824
Services			77,982			12,117		90,099		106,397		22,153		103,113		1,949
Wholesale and retail			160,477			12,218		172,695		189,231		62,962		186,594		3,076
Transportation and communications			55,202			3,833		59,035		61,554		18,870		54,633		1,220
Banks and other financial institutions			13,727			56		13,783		13,821		5,007		11,950		227
Other industries			5,224			140		5,364		5,484		3,818		4,791		73
Individuals			116,875			118,750		235,625		252,182		9,429		250,718		4,343
Total domestic			944,274			217,264		1,161,538		1,263,488		287,288		1,139,697		19,009
Foreign:
Total foreign			297,859			4,821		302,680		305,801		119,053		220,561		5,321
Total			1,242,133			222,085		1,464,218		1,569,289		406,341		1,360,258		24,330
2014
Domestic:
Manufacturing			216,579			12,291		228,870		240,660		74,367		259,889		4,086
Construction and real estate			107,932			29,981		137,913		163,813		30,724		183,437		2,213
Services			66,651			11,793		78,444		88,537		20,199		83,754		1,671
Wholesale and retail			142,886			13,014		155,900		172,641		51,274		161,288		2,795
Transportation and communications			44,237			3,851		48,088		54,149		14,691		50,387		939
Banks and other financial institutions			11,390			66		11,456		11,480		4,049		12,474		163
Other industries			781			80		861		2,020		108		3,486		19
Individuals			91,715			103,657		195,372		206,341		9,391		215,422		3,714
Total domestic			682,171			174,733		856,904		939,641		204,803		970,137		15,600
Foreign:
Total foreign			276,292			11,864		288,156		290,161		118,360		291,981		4,750
Total			958,463			186,597		1,145,060		1,229,802		323,163		1,262,118		20,350
Notes:
-1	Amounts represent the outstanding balances of nonaccrual loans. The MHFG Group’s policy for placing loans in nonaccrual status completely corresponds to the Group’s definition of impaired loans.
-2	These impaired loans do not require an allowance for loan losses because the MHFG Group has sufficient collateral to cover probable loan losses.
-3	The allowance for loan losses on impaired loans includes those for groups of small balance, homogeneous loans totaling ¥504,750 million and ¥425,391 million as of March 31, 2013 and 2014 which were collectively evaluated for impairment, in addition to those that were individually evaluated for impairment.
-4	Amounts represent gross interest income on impaired loans which were included in Interest income on loans in the consolidated statements of income.
The remaining balance of impaired loans which had been partially charged off were ¥51,720 million and ¥24,957 million as of March 31, 2013 and 2014, respectively.
Troubled debt restructurings
The MHFG Group considers restructurings, with respect to which concessions that it would not otherwise consider were granted to obligors in financial difficulty, as TDRs. The Group considers the relevant obligor to be in financial difficulty when its obligor rating is E2 or below. The following table presents TDRs that were made during the fiscal years ended March 31, 2013 and 2014.
		Loan forgiveness or debt to					Interest rate
		equity swaps					reduction and/or
							Postponement of
							principal and/or
		Recorded			Charge-offs (2)		interest
		investment (1)
					(in millions of yen)
2013
Domestic:
Manufacturing			—			—		277,957
Construction and real estate			—			—		129,908
Services			—			—		68,930
Wholesale and retail			—			1,243		218,497
Transportation and communications			—			—		52,206
Banks and other financial institutions			—			—		34,468
Other industries			—			—		1,809
Individuals			—			—		62,160
Total domestic			—			1,243		845,935
Foreign:
Total foreign			1,062			3,750		140,064
Total			1,062			4,993		985,999
2014
Domestic:
Manufacturing			235			481		196,705
Construction and real estate			2,528			136		44,573
Services			310			555		57,945
Wholesale and retail			5			149		170,217
Transportation and communications			—			—		34,598
Banks and other financial institutions			—			—		31,901
Other industries			—			—		1,998
Individuals			—			—		47,822
Total domestic			3,078			1,321		585,759
Foreign:
Total foreign			—			—		60,348
Total			3,078			1,321		646,107
Notes:
-1	Amounts represent the book values of loans immediately after the restructurings.
-2	Charge-offs represent the loss impact on the consolidated statements of income for the fiscal year that resulted from the restructurings.
Payment default is deemed to occur when the loan becomes three months past due or the obligor is downgraded to the category of substantially bankrupt or bankrupt. The following table presents payment defaults which occurred during the fiscal years ended March 31, 2013 and 2014 with respect to the loans modified as TDRs within the previous twelve months.
		Recorded investment
		2013			2014
		(in millions of yen)
Domestic:
Manufacturing			18,740			21,144
Construction and real estate			18,751			3,500
Services			5,976			3,707
Wholesale and retail			19,920			21,916
Transportation and communications			4,386			14,069
Banks and other financial institutions			—			—
Other industries			—			107
Individuals			5,517			6,283
Total domestic			73,290			70,726
Foreign:
Total foreign			6,374			115
Total			79,664			70,841
Age analysis of past due loans
The table below presents an analysis of the age of the recorded investment in loans that are past due at March 31, 2013 and 2014:
		30-59 days			60-89 days		90 days or		Total past		Current		Total
		past due			past due		more past due		due
		(in millions of yen)
2013
Domestic:
Manufacturing			3,788			1,911		32,830		38,529		8,040,342		8,078,871
Construction and real estate			11,815			4,038		69,333		85,186		7,392,667		7,477,853
Services			3,385			1,916		13,829		19,130		3,952,881		3,972,011
Wholesale and retail			2,771			2,851		16,483		22,105		5,333,869		5,355,974
Transportation and communications			711			558		3,687		4,956		3,142,150		3,147,106
Banks and other financial institutions			—			—		6		6		3,142,992		3,142,998
Government and public institutions			—			—		—		—		6,907,426		6,907,426
Other industries			—			18		122		140		4,521,854		4,521,994
Individuals			41,987			24,114		69,774		135,875		11,840,205		11,976,080
Total domestic			64,457			35,406		206,064		305,927		54,274,386		54,580,313
Foreign:
Total foreign			127			885		11,132		12,144		15,353,007		15,365,151
Total			64,584			36,291		217,196		318,071		69,627,393		69,945,464
2014
Domestic:
Manufacturing			2,834			2,193		14,452		19,479		8,006,453		8,025,932
Construction and real estate			5,412			3,440		44,852		53,704		7,150,890		7,204,594
Services			2,185			1,235		10,304		13,724		3,943,018		3,956,742
Wholesale and retail			3,205			4,561		12,180		19,946		5,330,761		5,350,707
Transportation and communications			832			573		3,265		4,670		3,242,724		3,247,394
Banks and other financial institutions			—			1		5		6		3,460,141		3,460,147
Government and public institutions			—			—		—		—		6,734,451		6,734,451
Other industries			9			29		34		72		4,983,749		4,983,821
Individuals			38,466			18,488		56,605		113,559		11,860,960		11,974,519
Total domestic			52,943			30,520		141,697		225,160		54,713,147		54,938,307
Foreign:
Total foreign			87			23		10,935		11,045		18,674,188		18,685,233
Total			53,030			30,543		152,632		236,205		73,387,335		73,623,540

Allowance_for_loan_losses

Allowance for loan losses	12 Months Ended
	Mar. 31, 2014
Allowance for loan losses	'
	5. Allowance for loan losses
	In accordance with ASC 450, a formula-based allowance utilizing historical loss factors, after adjusted for existing economic conditions where appropriate, is applied to groups of non-homogeneous loans and small balance, homogeneous loans which have not been identified as impaired. In MHBK and MHTB, when management estimates probable credit losses to determine the allowance for loan losses, small balance, homogeneous loans are classified in the retail portfolio segment to which pool allocations apply, and loans other than these classified in the retail portfolio segment are classified in the corporate portfolio segment. The corporate portfolio segment consists of loans originated by MHBK and MHTB, and includes mainly business loans such as those used for working capital and capital expenditure, as well as loans for which the primary source of repayment of the obligation is income generated by the relevant assets such as project finance, asset finance and real estate finance. The retail portfolio segment consists mainly of residential mortgage loans, originated by MHBK. The other portfolio segment consists of loans of subsidiaries other than MHBK and MHTB, such as consolidated VIEs and overseas subsidiaries. See Note 1 “Basis of presentation and summary of significant accounting policies” for further detail of the methodology used to determine the allowance for loan losses and Note 4 “Loans” for further details of obligor ratings and pool allocations.
	Changes in the Allowance for loan losses by portfolio segment for the fiscal years ended March 31, 2012, 2013 and 2014 are shown below:
		Corporate			Retail			Other		Total
		(in millions of yen)
	2012
	Balance at beginning of fiscal year		563,116			151,342			20,072		734,530
	Provision (credit) for loan losses		(19,433	)		(21,375	)		17,764		(23,044	)
	Charge-offs		54,599			5,133			20,410		80,142
	Less: Recoveries		48,354			1,442			2,460		52,256
	Net charge-offs		6,245			3,691			17,950		27,886
	Others (Note)		(1,963	)		—			1,055		(908	)
	Balance at end of fiscal year		535,475			126,276			20,941		682,692
	2013
	Balance at beginning of fiscal year		535,475			126,276			20,941		682,692
	Provision (credit) for loan losses		137,549			(14,180	)		16,578		139,947
	Charge-offs		69,845			4,249			20,503		94,597
	Less: Recoveries		27,447			1,342			2,911		31,700
	Net charge-offs		42,398			2,907			17,592		62,897
	Others (Note)		11,269			—			1,946		13,215
	Balance at end of fiscal year		641,895			109,189			21,873		772,957
	2014
	Balance at beginning of fiscal year		641,895			109,189			21,873		772,957
	Provision (credit) for loan losses		(128,368	)		(12,712	)		14,850		(126,230	)
	Charge-offs		47,927			3,935			13,286		65,148
	Less: Recoveries		21,423			3,000			2,112		26,535
	Net charge-offs		26,504			935			11,174		38,613
	Others (Note)		14,326			—			3,737		18,063
	Balance at end of fiscal year		501,349			95,542			29,286		626,177
	Note: Others include primarily foreign exchange translation.
	The table below presents the Allowance for loan losses and loans outstanding by portfolio segment disaggregated on the basis of impairment method at March 31, 2013 and 2014:
		Corporate			Retail			Other		Total
		(in millions of yen)
	2013
	Allowance for loan losses		641,895			109,189			21,873		772,957
	of which individually evaluated for impairment		398,622			14,815			9,247		422,684
	of which collectively evaluated for impairment		243,273			94,374			12,626		350,273
	Loans (Note)		51,801,814			13,007,792			5,135,858		69,945,464
	of which individually evaluated for impairment		1,160,489			45,961			59,974		1,266,424
	of which collectively evaluated for impairment		50,641,325			12,961,831			5,075,884		68,679,040
	2014
	Allowance for loan losses		501,349			95,542			29,286		626,177
	of which individually evaluated for impairment		327,011			11,735			10,562		349,308
	of which collectively evaluated for impairment		174,338			83,807			18,724		276,869
	Loans (Note)		54,651,867			12,922,564			6,049,109		73,623,540
	of which individually evaluated for impairment		1,100,938			39,250			54,127		1,194,315
	of which collectively evaluated for impairment		53,550,929			12,883,314			5,994,982		72,429,225
	Note: Amounts represent loan balances before deducting unearned income and deferred loan fees.
	In the fiscal year ended March 31, 2012, the Provision for loan losses decreased by ¥23,691 million from the previous fiscal year. The decrease was due primarily to upgrades in the obligor categories of a broad range of borrowers as a result of the effectiveness of the MHFG Group’s credit management activities which was enhanced against the backdrop of the improving domestic economic environment, reflecting the continuing gradual recovery of the Japanese economy.
	In the fiscal year ended March 31, 2013, the Provision for loan losses increased by ¥162,991 million from the previous fiscal year. The increase was due primarily to an increase in allowance for loan losses as a result of an increase in foreign impaired loans that required an allowance for loan losses and increased estimated losses reflecting changes in the business environment surrounding some domestic obligors, offset in part by the effects of the continuing gradual recovery of the Japanese economy.
	In the fiscal year ended March 31, 2014, the Provision for loan losses decreased by ¥266,177 million from the previous fiscal year. The decrease was due primarily to a decrease in allowance for loan losses on domestic impaired loans as a result of upgrades and collections related to some borrowers and non-impaired loans reflecting upgrades in the obligor categories of a broad range of borrowers mainly through our credit management activities, including business revitalization support for borrowers, reflecting the continuing gradual recovery of the Japanese economy.

Premises_and_equipment

Premises and equipment	12 Months Ended
	Mar. 31, 2014
Premises and equipment	'
	6. Premises and equipment
	Premises and equipment at March 31, 2013 and 2014 consist of the following:
		2013		2014
		(in millions of yen)
	Land		268,948		410,739
	Buildings		743,473		800,680
	Equipment and furniture		418,647		435,655
	Leasehold improvements		90,306		92,052
	Construction in progress		23,875		35,789
	Software		657,702		725,287
	Total		2,202,951		2,500,202
	Less: Accumulated depreciation and amortization		1,110,962		1,143,608
	Premises and equipment—net		1,091,989		1,356,594
	Depreciation and amortization expense for premises and equipment for the fiscal years ended March 31, 2012, 2013 and 2014 was ¥160,231 million, ¥151,550 million and ¥155,549 million, respectively.
	Premises and equipment under capital leases, which is primarily comprised of data processing equipment, amounted to ¥49,727 million and ¥51,681 million at March 31, 2013 and 2014, respectively. Accumulated depreciation and amortization on such premises and equipment at March 31, 2013 and 2014 amounted to ¥27,830 million and ¥28,209 million, respectively.

Goodwill_and_intangible_assets

Goodwill and intangible assets	12 Months Ended
	Mar. 31, 2014
Goodwill and intangible assets	'
	7. Goodwill and intangible assets
	Goodwill
	The changes in Goodwill during the fiscal years ended March 31, 2012, 2013 and 2014 were as follows:
			MHBK			Total
			(in millions of yen)
	2012
	Balance at beginning of fiscal year			7,610			7,610
	Goodwill acquired (1)			3,776			3,776
	Impairment losses recognized			5,637			5,637
	Foreign exchange translation			(114	)		(114	)
	Balance at end of fiscal year			5,635			5,635
	Gross amount of goodwill			70,909			70,909
	Accumulated impairment losses			65,274			65,274
	2013
	Balance at beginning of fiscal year			5,635			5,635
	Goodwill acquired			—			—
	Impairment losses recognized			—			—
	Foreign exchange translation			512			512
	Balance at end of fiscal year			6,147			6,147
	Gross amount of goodwill			71,421			71,421
	Accumulated impairment losses			65,274			65,274
	2014
	Balance at beginning of fiscal year			6,147			6,147
	Goodwill acquired (2)			7,719			7,719
	Impairment losses recognized			3,792			3,792
	Foreign exchange translation			1,475			1,475
	Balance at end of fiscal year			11,549			11,549
	Gross amount of goodwill			80,615			80,615
	Accumulated impairment losses			69,066			69,066
	Notes:
	-1	Goodwill acquired is entirely related to the acquisition of PT. Mizuho Balimor Finance.
	-2	Goodwill acquired is entirely related to the acquisition of Banco Mizuho do Brasil S.A.
	Due to the prolonged severe business environment for the former Mizuho Investors Securities Co., Ltd. (“MHIS”) and PT. Mizuho Balimor Finance, it was determined that the carrying amounts of the former MHIS reporting unit and PT. Mizuho Balimor Finance reporting unit exceeded their fair values, and therefore, goodwill impairment losses of ¥5,637 million and ¥3,792 million related to the former MHIS and PT. Mizuho Balimor Finance were recognized during the fiscal years ended March 31, 2012 and 2014, respectively.
	Intangible assets
	The table below presents the gross carrying amount, accumulated amortization and net carrying amount of intangible assets, at March 31, 2013 and 2014.
			2013								2014
			Gross			Accumulated			Net		Gross		Accumulated		Net
			carrying			amortization			carrying		carrying		amortization		carrying
			amount						amount		amount				amount
			(in millions of yen)
	Intangible assets subject to amortization:
	Customer relationships (Note)			73,949			19,238			54,711		73,949		24,865		49,084
	Other			2,363			2,050			313		2,808		2,152		656
	Total			76,312			21,288			55,024		76,757		27,017		49,740
	Intangible assets not subject to amortization:
	Total			9,450			—			9,450		9,207		—		9,207
	Total			85,762			21,288			64,474		85,964		27,017		58,947
	Note:	Customer relationships were acquired by the merger of MHSC and Shinko on May 7, 2009. See Note 1 “Basis of presentation and summary of significant accounting policies” for further information.
	For the fiscal years ended March 31, 2012, 2013, and 2014, the MHFG Group recognized ¥5,490 million, ¥5,615 million, and ¥5,709 million, respectively, of amortization expenses for intangible assets.
	The table below presents the estimated aggregate amortization expenses for intangible assets for the next five years:
			(in millions of yen)
	Fiscal year ending March 31:
	2015			5,349
	2016			5,058
	2017			4,780
	2018			4,502
	2019			4,264

Pledged_assets_and_collateral

Pledged assets and collateral	12 Months Ended
	Mar. 31, 2014
Pledged assets and collateral	'
	8. Pledged assets and collateral
	The following amounts, by balance sheet classification, have been pledged as collateral for borrowings and for other purposes at March 31, 2013 and 2014:
		2013		2014
		(in billions of yen)
	Interest-bearing deposits in other banks		28		38
	Trading account assets		13,752		10,271
	Available-for-sale securities		15,939		13,353
	Loans		8,860		8,796
	Other assets		900		677
	Total		39,479		33,135
	The associated liabilities collateralized by the above assets at March 31, 2013 and 2014 are summarized below:
		2013		2014
		(in billions of yen)
	Deposits		259		878
	Call money and funds purchased		1,580		1,708
	Payables under repurchase agreements		7,726		6,884
	Payables under securities lending transactions		11,092		6,237
	Other short-term borrowings		5,626		405
	Long-term debt		321		5,632
	Total		26,604		21,744
	The Bank of Japan (“the BOJ”) requires private depository institutions to maintain a certain amount of funds as reserves in current accounts with the BOJ, based on average deposit balances and certain other factors. There are similar reserve deposit requirements for foreign branches and subsidiaries engaged in banking businesses in foreign countries. At March 31, 2013 and 2014, the deposit amounts maintained with the BOJ and foreign central banks, which were included in Cash and due from banks and Interest-bearing deposits in other banks, were ¥10,507 billion and ¥18,084 billion, respectively. Those balances included the reserve funds required to be maintained by the MHFG Group, which amounted to ¥1,099 billion and ¥1,184 billion at March 31, 2013 and 2014, respectively.
	At March 31, 2013 and 2014, the MHFG Group had received collateral that can be sold or repledged, with a fair value of ¥15,501 billion and ¥13,817 billion, respectively, of which ¥13,834 billion and ¥12,508 billion, respectively, were sold or repledged. Such collateral was primarily obtained under resale or securities borrowing agreements, and was used generally as collateral under repurchase or securities lending agreements, or to cover short sales.

Deposits

Deposits	12 Months Ended
	Mar. 31, 2014
Deposits	'
	9. Deposits
	The balances of time deposits and certificates of deposit issued by domestic offices in amounts of ¥10 million (approximately US$97 thousand at the Federal Reserve Bank of New York’s noon buying rate on March 31, 2014) or more and the balances of those deposits issued by foreign offices in amounts of US$100,000 or more at March 31, 2013 and 2014 are as follows:
		2013		2014
		(in millions of yen)
	Domestic offices:
	Time deposits		18,302,196		18,351,826
	Certificates of deposit		11,393,094		8,117,512
	Total		29,695,290		26,469,338
	Foreign offices:
	Time deposits		8,209,016		9,555,568
	Certificates of deposit		3,933,688		4,638,265
	Total		12,142,704		14,193,833
	The aggregate amount of demand deposits in overdraft status that have been reclassified as loan balances at March 31, 2013 and 2014 was ¥543 billion and ¥597 billion, respectively.
	The balance and remaining maturities of time deposits and certificates of deposit issued by domestic and foreign offices at March 31, 2014 are shown in the following table:
		Time		Certificates of		Total
		deposits		deposit
		(in millions of yen)
	Domestic offices:
	Due in one year or less		24,079,640		8,115,532		32,195,172
	Due after one year through two years		1,910,790		1,980		1,912,770
	Due after two years through three years		1,243,980		—		1,243,980
	Due after three years through four years		342,948		—		342,948
	Due after four years through five years		412,261		—		412,261
	Due after five years		133,735		—		133,735
	Total		28,123,354		8,117,512		36,240,866
	Foreign offices:
	Due in one year or less		9,526,641		4,630,546		14,157,187
	Due after one year through two years		20,176		7,719		27,895
	Due after two years through three years		9,528		—		9,528
	Due after three years through four years		1,102		—		1,102
	Due after four years through five years		3,240		—		3,240
	Due after five years		392		—		392
	Total		9,561,079		4,638,265		14,199,344
	Total		37,684,433		12,755,777		50,440,210

Due_to_trust_accounts

Due to trust accounts	12 Months Ended
	Mar. 31, 2014
Due to trust accounts	'
	10. Due to trust accounts
	MHTB and TCSB, which are MHFG’s trust bank subsidiaries, hold assets on behalf of their customers in an agent, fiduciary or trust capacity. Such trust account assets are not the MHFG Group’s proprietary assets and are managed and accounted for separately. However, the cash in individual trust accounts is often placed with MHTB and TCSB for the customers’ short-term investment needs. These amounts which MHTB and TCSB owe to the trust accounts are recorded as Due to trust accounts.
	The MHFG Group consolidates certain guaranteed principal money trusts. See Note 25 “Variable interest entities and securitizations” for further discussion of the guaranteed principal money trust.

Shortterm_borrowings_and_longt

Short-term borrowings and long-term debt	12 Months Ended
	Mar. 31, 2014
Short-term borrowings and long-term debt	'
	11. Short-term borrowings and long-term debt
	Short-term borrowings
	Short-term borrowings consist of Due to trust accounts, Call money and funds purchased, Payables under repurchase agreements and securities lending transactions, and Other short-term borrowings.
	Details of Other short-term borrowings at March 31, 2013 and 2014 are as follows:
			2013		2014
			(in millions of yen)
	Commercial paper and short-term notes issued by consolidated VIEs of asset-backed commercial paper programs (1) (2)			252,277		286,968
	Short-term notes issued by MHFG and its subsidiaries (1)			477,400		497,100
	Borrowings from the Bank of Japan			5,884,304		5,138,003
	Other			110,119		101,901
	Total			6,724,100		6,023,972
	Notes:
	-1	Short-term notes are issued under laws of Japan in the form of dematerialized commercial paper, whose characteristics are economically the same as commercial paper.
	-2	Commercial paper and short-term notes issued by consolidated VIEs of asset-backed commercial paper programs in the above table consist of commercial paper and short-term notes, of which amounts were ¥164,194 million and ¥88,083 million, respectively, at March 31, 2013, and ¥199,500 million and ¥87,468 million, respectively, at March 31, 2014.
	Long-term debt
	Long-term debt with original maturities of more than one year at March 31, 2013 and 2014 is comprised of the following:
			2013		2014
			(in millions of yen)
	Obligations under capital leases			24,406		26,680
	Loan participation borrowings			62,332		79,014
	Senior borrowings and bonds			4,784,010		5,805,634
	Subordinated borrowings and bonds			3,931,475		3,942,613
	Total			8,802,223		9,853,941
	The following table presents the interest rates and maturities of senior borrowings and bonds, and subordinated borrowings and bonds:
			Interest rates (1)		Maturities (2)		2013		2014
			(%)				(in millions of yen)
	Senior borrowings and bonds:
	fixed rate denominated in Japanese yen			0.00-10.00		Apr. 2014-Mar. 2044		2,741,475		3,557,508
	fixed rate denominated in U.S. dollars			0.00-7.49		Apr. 2014-Jul. 2043		520,714		604,281
	fixed rate denominated in other currencies			0.02-5.40		Jan. 2015-Mar. 2029		683		25,687
	floating rate denominated in Japanese yen			0.00-18.10		Apr. 2014-Mar. 2044		1,065,708		1,063,111
	floating rate denominated in U.S. dollars			0.00-15.60		Apr. 2014-Mar. 2028		426,515		532,199
	floating rate denominated in other currencies			0.05-0.58		Apr. 2014-Jan. 2015		28,915		22,848
	Total							4,784,010		5,805,634
	Subordinated borrowings and bonds:
	fixed rate denominated in Japanese yen			1.09-4.74		Apr. 2014-Perpetual		3,393,092		3,249,999
	fixed rate denominated in U.S. dollars			4.30-14.91		Apr. 2014-Perpetual		419,383		613,609
	floating rate denominated in Japanese yen			0.98-2.61		Jun. 2019-Perpetual		119,000		79,005
	Total							3,931,475		3,942,613
	Total							8,715,485		9,748,247
	Notes:
	-1	The interest rates disclosed reflect the range of contractual rates in effect at March 31, 2014.
	-2	Maturity information disclosed is the range of maturities at March 31, 2014.
	-3	None of the long-term debt issuances above are convertible to common stock.
	-4	Certain debt agreements permit the MHFG Group to redeem the related debt, in whole or in part, prior to maturity at the MHFG Group’s option on terms specified in the respective agreements.
	The following is a summary of the contractual maturities of long-term debt subsequent to March 31, 2014:
			(in millions of yen)
	Fiscal year ending March 31:
	2015			1,222,317
	2016			1,190,985
	2017			1,776,546
	2018			1,025,441
	2019			483,888
	2020 and thereafter			4,154,764
	Total			9,853,941

Other_assets_and_liabilities

Other assets and liabilities	12 Months Ended
	Mar. 31, 2014
Other assets and liabilities	'
	12. Other assets and liabilities
	The following table sets forth the details of other assets and liabilities at March 31, 2013 and 2014:
		2013		2014
		(in millions of yen)
	Other assets:
	Accounts receivable from brokers, dealers and customers for securities transactions		907,671		1,122,247
	Collateral provided for derivative transactions		742,307		466,420
	Prepaid pension cost		153,414		403,654
	Miscellaneous receivables		120,322		315,037
	Margins provided for futures contracts		99,844		147,376
	Security deposits		102,031		121,675
	Loans held for sale		9,820		58,745
	Other		466,542		563,841
	Total		2,601,951		3,198,995
	Other liabilities:
	Accounts payable to brokers, dealers and customers for securities transactions		1,560,345		1,325,455
	Guaranteed trust principal		535,720		591,647
	Miscellaneous payables		260,665		473,028
	Collateral accepted for derivative transactions		503,101		432,820
	Factoring amounts owed to customers		375,933		382,189
	Margins accepted for futures contracts		199,930		289,381
	Unearned income		141,189		141,735
	Other		791,243		785,768
	Total		4,368,126		4,422,023
	Unearned income
	Unearned income is primarily comprised of refundable fees received from consumer loan customers at the time the loan was made, which is being deferred and recognized in earnings as earned.
	Guaranteed trust principal
	Guaranteed trust principal is the liability of certain consolidated trust arrangements, which the MHFG Group provides guarantees for the repayment of principal. See Note 25 “Variable interest entities and securitizations” for further discussion of the guaranteed principal money trust.

Preferred_stock

Preferred stock	12 Months Ended
	Mar. 31, 2014
Preferred stock	'
	13. Preferred stock
	The composition of preferred stock at March 31, 2012, 2013 and 2014 is as follows:
	2012		Aggregate amount			Number of shares						Liquidation		Convertible
	Class of stock					Authorized		Issued		In treasury		value per share		or not
			(in millions of yen)									(in yen)
	Eleventh series class XI preferred stock (1)			914,752			1,369,512,000		914,752,000		541,073,800		1,000		Yes
	Class XII preferred stock			—			1,500,000,000		—		—		—		—
	Thirteenth series class XIII preferred stock			36,690			1,500,000,000		36,690,000		—		1,000		No
	Total			951,442			4,369,512,000		951,442,000		541,073,800
	2013		Aggregate amount			Number of shares						Liquidation		Convertible
	Class of stock					Authorized		Issued		In treasury		value per share		or not
			(in millions of yen)									(in yen)
	Eleventh series class XI preferred stock (1)			914,752			1,369,512,000		914,752,000		574,087,800		1,000		Yes
	Class XII preferred stock			—			1,500,000,000		—		—		—		—
	Thirteenth series class XIII preferred stock			36,690			1,500,000,000		36,690,000		—		1,000		No
	Total			951,442			4,369,512,000		951,442,000		574,087,800
	2014		Aggregate amount			Number of shares						Liquidation		Convertible
	Class of stock					Authorized		Issued		In treasury		value per share		or not
			(in millions of yen)									(in yen)
	Eleventh series class XI preferred stock (1)			914,752			914,752,000		914,752,000		602,100,700		1,000		Yes
	Thirteenth series class XIII preferred stock			—			36,690,000		—		—		—		—
	First series class XIV preferred stock (2)			—			900,000,000		—		—		—		—
	Second series class XIV preferred stock (2)			—			900,000,000		—		—		—		—
	Third series class XIV preferred stock (2)			—			900,000,000		—		—		—		—
	Fourth series class XIV preferred stock (2)			—			900,000,000		—		—		—		—
	First series class XV preferred stock (3)			—			900,000,000		—		—		—		—
	Second series class XV preferred stock (3)			—			900,000,000		—		—		—		—
	Third series class XV preferred stock (3)			—			900,000,000		—		—		—		—
	Fourth series class XV preferred stock (3)			—			900,000,000		—		—		—		—
	First series class XVI preferred stock (4)			—			1,500,000,000		—		—		—		—
	Second series class XVI preferred stock (4)			—			1,500,000,000		—		—		—		—
	Third series class XVI preferred stock (4)			—			1,500,000,000		—		—		—		—
	Fourth series class XVI preferred stock (4)			—			1,500,000,000		—		—		—		—
	Total			914,752			4,251,442,000		914,752,000		602,100,700
	Notes:
	-1	The aggregate amount and number of issued shares include the preferred stock in treasury which has been converted to common stock but not yet cancelled.
	-2	The total number of authorized shares from first to fourth series class XIV preferred stock shall not exceed 900,000,000.
	-3	The total number of authorized shares from first to fourth series class XV preferred stock shall not exceed 900,000,000.
	-4	The total number of authorized shares from first to fourth series class XVI preferred stock shall not exceed 1,500,000,000.
	Holders or registered pledgees of preferred stock are entitled to receive annual dividends, and distribution of residual assets of MHFG as set out above at the liquidation value per share, prior to holders of common stock but pari passu among themselves. MHFG may pay up to one-half of the annual dividend payable on each class of preferred stock as an interim dividend. Dividends on preferred stock are not cumulative. Holders of preferred stock are not entitled to vote at a general meeting of shareholders except where the articles of incorporation entitle holders of preferred stock to vote.
	In June 2013, MHFG newly authorized class XIV preferred stock, class XV preferred stock and class XVI preferred stock in relation to meet the requirements of Basel III. Under Basel III, in order for preferred stock issued by a bank holding company to be included as its regulatory capital under the capital adequacy requirements, the terms and conditions of the preferred stock are required to include a provision that in the case where the bank holding company is recognized as non-viable, (1) a write-off of the relevant preferred stock or (2) a conversion of the relevant preferred stock into common stock shall be effected (a loss-absorption clause). In respect of class XI preferred stock, class XII preferred stock and class XIII preferred stock, which were authorized for since before the implementation of Basel III in the articles of incorporation of MHFG, it is not possible to include the foregoing loss-absorption clause in the terms and conditions of those preferred stock under the current provisions of the articles of incorporation. Therefore, class XIV preferred stock, class XV preferred stock and class XVI preferred stock were newly authorized so that the foregoing loss-absorption clause can be included in the terms and conditions of class XIV preferred stock, class XV preferred stock and class XVI preferred stock by a resolution of the board of directors relating to the issuance of the relevant preferred stock. Besides the foregoing loss-absorption clause, provisions regarding the preferred stock dividends, distribution of residual assets, acquisition clause and rights to request acquisition in respect of class XIV preferred stock, class XV preferred stock and class XVI preferred stock were newly established. In addition, each of class XIV preferred stock, class XV preferred stock and class XVI preferred stock was established in multiple series as a separate class of shares in order to enable MHFG to issue those preferred stock in multiple series.
	Eleventh series class XI preferred stock is convertible into common stock at the option of the holder. The material terms and conditions of conversion are as follows.
			Conversion period		Conversion ratio (Note)
	Eleventh series class XI preferred stock		July 1, 2008 to		¥1,000/(conversion price), where the conversion price after adjustment is ¥282.90 on or after August 30, 2011; to be reset on July 1, 2014 and 2015 (each, a “Reset Date”) as ¥1,000/(conversion price), where the conversion price is the lower of (x) the average price of daily closing prices (including closing bid or offered price) of common stock as reported by the Tokyo Stock Exchange (“TSE”) for the 30 consecutive trading days (excluding trading days on which no closing price, closing bid or offered price is reported) commencing on the 45th trading day prior to the Reset Date and (y) the conversion price after adjustment effective as of the day before the relevant Reset Date, provided that the conversion price shall not be less than ¥282.90.
			30-Jun-16
	Note:	Subject to adjustment, where issuance or disposal by MHFG of common stock for a price below the “current market price”, a stock split, issuance of securities convertible into common stock at a price below the “current market price” at the time of issuance thereof or determination of the conversion price thereof, merger or amalgamation, or a capital decrease or stock consolidation occurs and in certain other circumstances.
	Each share of preferred stock which has not been converted as described above by the end of the relevant conversion period will be converted into common stock on the day following the end of the conversion period on the following terms:
			Conversion date		Conversion ratio
	Eleventh series class XI preferred stock		1-Jul-16		¥1,000/(current market price), where the current market price is the average price of daily closing prices (including closing bid or offered price) of common stock as reported by the TSE for the 30 consecutive trading days (excluding trading days on which no closing price, closing bid or offered price is reported) commencing on the 45th trading day prior to July 1, 2016, provided that the current market price shall not be less than ¥282.90.
	The changes in the number of shares and the aggregate amount of preferred stock during the fiscal years ended March 31, 2012, 2013 and 2014 were as follows:
	Class of stock		Issued at			Net		Issued at		Net		Issued at		Net			Issued at
			March 31,			change		March 31,		change		March 31,		change			March 31,
			2011					2012				2013					2014
			(number of shares)
	Eleventh series class XI preferred stock (Note)			914,752,000			—		914,752,000		—		914,752,000		—			914,752,000
	Thirteenth series class XIII preferred stock			36,690,000			—		36,690,000		—		36,690,000		(36,690,000	)		—
	Total			951,442,000			—		951,442,000		—		951,442,000		(36,690,000	)		914,752,000
	Class of stock		Aggregate			Net		Aggregate		Net		Aggregate		Net			Aggregate
			amount at			change		amount at		change		amount at		change			amount at
			March 31,					March 31,				March 31,					March 31,
			2011					2012				2013					2014
			(in millions of yen)
	Eleventh series class XI preferred stock (Note)			914,752			—		914,752		—		914,752		—			914,752
Thirteenth series class XIII preferred stock			36,690			—		36,690		—		36,690		(36,690	)		—
Total			951,442			—		951,442		—		951,442		(36,690	)		914,752
Note:	The aggregate amount and number of issued shares include the preferred stock in treasury which has been converted to common stock but not yet cancelled.

Common_stock

Common stock	12 Months Ended
	Mar. 31, 2014
Common stock	'
	14. Common stock
	On September 1, 2011, MHFG exchanged 824,271,984 shares of its common stock for 30.15 percent of the voting equity interests in MHTB, in order to turn MHTB into MHFG’s wholly-owned subsidiary. This transaction was accounted for as an equity transaction. The consideration through issuance of common stock was ¥95,828 million and the MHFG Group recognized a decrease of ¥65,494 million in additional paid-in capital which reflects the adjustment to the carrying amount of Noncontrolling interests. In addition, the carrying amount of Accumulated other comprehensive income of ¥958 million was adjusted to reflect the change in the ownership interest in MHTB through a corresponding increase in additional paid-in capital.
	On September 1, 2011, the former MHCB exchanged 951,166,005 shares of MHFG’s common stock for 40.80 percent of the voting equity interests in the former MHSC, in order to turn the former MHSC into the former MHCB’s wholly-owned subsidiary. This transaction was accounted for as an equity transaction. The consideration through issuance of common stock was ¥110,379 million and the Group recognized increase of ¥38,423 million in additional paid-in capital which reflects the adjustment to the carrying amount of Noncontrolling interests. In addition, the carrying amount of Accumulated other comprehensive income of ¥2,178 million was adjusted to reflect the change in the ownership interest in the former MHSC through a corresponding decrease in additional paid-in capital.
	On September 1, 2011, the former MHBK exchanged 322,928,897 shares of MHFG’s common stock for 46.02 percent of the voting equity interests in the former MHIS, in order to turn the former MHIS into the former MHBK’s wholly-owned subsidiary. This transaction was accounted for as an equity transaction. The consideration through issuance of common stock was ¥37,497 million and the Group recognized increase of ¥11,599 million in additional paid-in capital which reflects the adjustment to the carrying amount of Noncontrolling interests. In addition, the carrying amount of Accumulated other comprehensive income of ¥744 million was adjusted to reflect the change in the ownership interest in the former MHIS through a corresponding increase in additional paid-in capital.
	The changes in the number of issued shares of common stock during the fiscal years ended March 31, 2012, 2013 and 2014 were as follows:
		2012		2013		2014
		(shares)
	Balance at beginning of fiscal year		21,782,185,320		24,048,165,727		24,164,864,477
	Issuance of new shares of common stock by conversion of Eleventh series class XI preferred stock		151,921,540		116,698,750		99,020,710
	Issuance of new shares of common stock by exercise of stock acquisition rights		4,748,000		—		—
	Issuance of new shares of common stock for stock exchanges		2,109,310,867		—		—
	Balance at end of fiscal year		24,048,165,727		24,164,864,477		24,263,885,187

Dividends

Dividends	12 Months Ended
	Mar. 31, 2014
Dividends	'
	15. Dividends
	The amount available for dividends under the Companies Act is based on the amount recorded in MHFG’s non-consolidated general books of account, maintained in accordance with accounting principles generally accepted in Japan (“Japanese GAAP”) and adjusted by post period-end changes. Therefore, the consolidated shareholders’ equity under U.S. GAAP has no effect on the determination of the amount available for dividends. On March 31, 2014, MHFG’s capital stock, capital surplus and retained earnings were ¥2,254,973 million, ¥1,194,865 million and ¥1,419,866 million, respectively, under Japanese GAAP.
	In making a distribution of retained earnings, an entity must set aside in its legal reserve an amount equal to one-tenth of the amount of retained earnings so distributed, until its legal reserve reaches to one-quarter of its capital stock. MHFG’s legal reserve at March 31, 2014 was ¥1,199,215 million, of which ¥1,194,865 million was included in capital surplus and ¥4,350 million in retained earnings.
	In addition to the provision that requires an appropriation for the legal reserve, the Companies Act and the Banking Act impose certain limitations on the amount available for dividends. Under the Companies Act, MHFG’s maximum amount available for dividends, at March 31, 2014, was ¥1,412,282 million, based on the amount recorded in MHFG’s general books of account under Japanese GAAP. Under the Banking Act and related regulations, MHFG has to meet the minimum capital adequacy requirements. Distributions of retained earnings, which are otherwise distributable to shareholders, are restricted in order to maintain the minimum Common Equity Tier 1 capital ratio of 4.5% (3.5% in 2013 and 4.0% in 2014) for capital adequacy purposes under the rules in Basel III. See Note 17 “Regulatory matters” for further discussion of regulatory capital requirements.
	Payment of dividends on shares of common stock is also subject to the prior payment of dividends on shares of preferred stock.
	Dividends on preferred stock and common stock during the fiscal years ended March 31, 2012, 2013 and 2014 were as follows:
	2012		Cash dividends (1)
	Class of stock		Per share		In aggregate (2)
			(in yen)		(in millions of yen)
	Eleventh series class XI preferred stock			30		12,173
	Thirteenth series class XIII preferred stock			45		1,651
	Common stock			9		202,684
	Total					216,508
	2013		Cash dividends
	Class of stock		Per share		In aggregate (2)
			(in yen)		(in millions of yen)
	Eleventh series class XI preferred stock			20		7,451
	Thirteenth series class XIII preferred stock			30		1,101
	Common stock			6		144,170
	Total					152,722
	2014		Cash dividends
	Class of stock		Per share		In aggregate (2)
			(in yen)		(in millions of yen)
	Eleventh series class XI preferred stock			20		6,717
	Thirteenth series class XIII preferred stock (3)			15		550
	Common stock			6		144,998
	Total					152,265
	Notes:
	-1	As MHFG commenced distributing an interim dividend from the fiscal year ended March 31, 2012, the amounts for the fiscal year include such interim dividends.
	-2	Dividends paid on treasury stock are excluded.
	-3	On July 11, 2013, MHFG acquired and cancelled all of the shares of the thirteenth series class XIII preferred stock. Consequently, the amount for the fiscal year does not include interim dividends.

Accumulated_other_comprehensiv

Accumulated other comprehensive income (loss)	12 Months Ended
	Mar. 31, 2014
Accumulated other comprehensive income (loss)	'
	16. Accumulated other comprehensive income (loss)
	Changes in each component of AOCI for the fiscal years ended March 31, 2012, 2013 and 2014 are as follows:
			2012			2013			2014
			(in millions of yen)
	AOCI, balance at beginning of fiscal year			104,972			245,588			777,997
	Unrealized net gains (losses) on available-for-sale securities:
	Balance at beginning of fiscal year			514,128			628,636			995,124
	Unrealized holding gains (losses) during year			87,215			427,913			255,140
	Less: reclassification adjustments for losses (gains) included in net income			27,293			(61,425	)		(126,992	)
	Change during year			114,508			366,488			128,148
	Balance at end of fiscal year			628,636			995,124			1,123,272
	Foreign currency translation adjustments:
	Balance at beginning of fiscal year			(165,028	)		(169,881	)		(82,420	)
	Foreign currency translation adjustments during year			(6,779	)		87,460			75,986
	Less: reclassification adjustments for losses (gains) included in net income			1,926			1			—
	Change during year			(4,853	)		87,461			75,986
	Balance at end of fiscal year			(169,881	)		(82,420	)		(6,434	)
	Pension liability adjustments:
	Balance at beginning of fiscal year			(244,128	)		(213,167	)		(134,707	)
	Unrealized gains (losses) during year			14,711			67,795			131,360
	Less: reclassification adjustments for losses (gains) included in net income			16,250			10,665			4,386
	Change during year			30,961			78,460			135,746
	Balance at end of fiscal year			(213,167	)		(134,707	)		1,039
	Total other comprehensive income (loss), net of tax attributable to MHFG shareholders			140,616			532,409			339,880
	AOCI, balance at end of fiscal year			245,588			777,997			1,117,877
	The following table shows the amounts reclassified out of AOCI into net income during the fiscal year ended March 31, 2014.
			Before			Tax			Net of tax			Net of tax			Net of tax
			tax (1)			effect (2)			before			attributable to			attributable to
									allocation to			noncontrolling			MHFG
									noncontrolling			interests (2)			shareholders
									interests
			(in millions of yen)
	Amounts reclassified out of AOCI into net income:																	Affected line items in the consolidated statements of income:
	Unrealized net gains (losses) on available-for-sale securities			197,224			(70,228	)		126,996			4			126,992		Investment gains (losses)—net
	Foreign currency translation adjustments			—			—			—			—			—
	Pension liability adjustments			(6,877	)		2,442			(4,435	)		(49	)		(4,386	)	Salaries and employee benefits
	Total			190,347			(67,786	)		122,561			(45	)		122,606
	Notes:
	-1	The amounts in the Before tax column are recorded in each account presented as “Affected line items in the consolidated statements of income”.
	-2	The amounts in the Tax effect column and Net of tax attributable to noncontrolling interests column are recorded in Income tax expense and Net income attributable to noncontrolling interests in the consolidated statements of income respectively.

Regulatory_matters

Regulatory matters	12 Months Ended
	Mar. 31, 2014
Regulatory matters	'
	17. Regulatory matters
	Regulatory capital requirements
	MHFG, MHBK, and MHTB are subject to regulatory capital requirements administered by the Financial Services Agency in accordance with the provisions of the Banking Act and related regulations. Failure to meet minimum capital requirements may initiate certain mandatory actions by regulators that, if undertaken, could have a direct material effect on the MHFG Group’s consolidated financial condition and results of operations.
	The capital adequacy guidelines applicable to Japanese banks and bank holding companies with international operations supervised by the Financial Services Agency closely follow the risk-adjusted approach proposed by the Bank for International Settlements (“BIS”) and are intended to further strengthen the soundness and stability of Japanese banks. Effective March 31, 2007, guidelines were implemented by the Financial Services Agency to comply with the capital adequacy requirements set by BIS called Basel II. The framework of Basel II is based on the following three pillars: minimum capital requirements; supervisory review; and market discipline.
	In May 2011, the capital adequacy guidelines were revised by the Financial Services Agency to comply with the package of measures to enhance the Basel II framework approved by the Basel Committee on Banking Supervision in July 2009. The revised guidelines include the strengthening of rules governing trading book capital and the strengthening of treatment of certain securitizations under the first pillar. The revised guidelines have been effective since the end of December 2011.
	In December 2010, the Basel Committee on Banking Supervision issued the Basel III rules text (later revised in June 2011 and January 2013), which presents the details of global regulatory standards on bank capital adequacy and liquidity agreed by the Governors and Heads of Supervision, which is the oversight body of the Basel Committee on Banking Supervision, and endorsed by the G20 Leaders at the Seoul summit in November 2010. The rules text sets out higher and better-quality capital, better risk coverage, the introduction of a leverage ratio as a backstop to the risk-based requirement, measures to promote the build-up of capital that can be drawn down in periods of stress, and the introduction of two global liquidity standards. The Financial Services Agency’s revisions to its capital adequacy guidelines became effective from March 31, 2013, which generally reflect rules in the Basel III rules text that have been applied from January 1, 2013. While the three-pillar structure of Basel II has been retained, Basel III includes various changes as described further below.
	Under the first pillar, the capital ratio is calculated by dividing regulatory capital, or risk-based capital, by risk-weighted assets. With respect to the calculation of risk-weighted assets, the MHFG Group adopts the advanced internal ratings-based approach. Under such approach, balance sheet assets and off-balance sheet exposures, calculated under Japanese GAAP, are assessed in terms of credit risk according to risk components such as probability of default and loss given default, which are derived from the Group’s own internal credit experience. In addition to credit risk, banks are required to measure and apply capital charges with respect to their market risks. Market risk is defined as the risk of losses in on- and off-balance-sheet positions arising from movements in market prices. Operational risk, which was introduced under Basel II with respect to regulatory capital requirements, is the risk of loss resulting from inadequate or failed internal processes, people and systems, or from external events. The Group adopts the advanced measurement approach for the measurement of operational risk equivalent by taking account of the following four elements: internal loss data; external loss data; scenario analysis; and business environment and internal control factors. Under Basel III, the calculation method of risk-weighted assets was revised, including modification to the treatment of counterparty credit risk, such as a capital charge for credit valuation adjustment risk.
	With regard to risk-based capital, the guidelines based on Basel III set out higher and better-quality capital standards compared to those under Basel II. The guidelines based on Basel III require a target minimum standard capital adequacy ratio of 8%, Tier 1 capital ratio of 6% (phased in at 4.5% in 2013 and 5.5% in 2014) and Common Equity Tier 1 capital ratio of 4.5% (phased in at 3.5% in 2013 and 4.0% in 2014), on both a consolidated and non-consolidated basis for banks with international operations, such as MHBK and MHTB, or on a consolidated basis for bank holding companies with international operations, such as MHFG.
	Risk-based capital, calculated from financial statements prepared under Japanese GAAP, is classified into the following two tiers: Tier 1 capital; and Tier 2 capital. Tier 1 capital consists of Common Equity Tier 1 capital and Additional Tier 1 capital. Common Equity Tier 1 capital generally consists of common stock, capital surplus, retained earnings, accumulated other comprehensive income and other disclosed reserves and others less any regulatory adjustments. Additional Tier 1 capital generally consists of instruments issued by a bank or its holding company that meet the criteria for inclusion in Additional Tier 1 capital and others less any regulatory adjustments. Tier 2 capital generally consists of instruments issued by a bank or its holding company such as subordinated debt that meet the criteria for inclusion in Tier 2 capital, general reserve for possible losses on loans, equaling the sum of (i) the excess of the amount of qualified reserves over the amount of expected losses and (ii) the amount of general reserves calculated based on the standardized approach, and others less any regulatory adjustments.
	The minimum requirement for Common Equity Tier 1 capital will be raised in phases from 3.5% of risk-weighted assets in March 2013 to 4.5% when fully effective in March 2015. Thereafter, a capital conservation buffer, to be met with Common Equity Tier 1 capital, is expected to be phased in beginning March 2016 at 0.625% until becoming fully effective in March 2019 at 2.5%, although the capital adequacy guidelines related to the capital conservation buffer have not yet been published by the Financial Services Agency. Thus the Common Equity Tier 1 capital requirement, including capital conservation buffer, is expected to be 7.0% beginning March 2019. In addition, subject to national discretion by the respective regulatory authorities, a countercyclical buffer ranging from 0% to 2.5%, consisting of Common Equity Tier 1 capital or other fully loss absorbing capital, would also be imposed on banking organizations through an extension of the capital conservation buffer when the relevant national authority judges a period of excess credit growth to be leading to the build-up of system-wide risk. The countercyclical buffer for internationally active banks will be a weighted average of the buffers deployed across all the jurisdictions to which it has credit exposures. Moreover, capital instruments that will no longer qualify as Additional Tier 1 capital or Tier 2 capital under Basel III is being phased out beginning March 2013 by increments of 10% until becoming fully effective in March 2022. The MHFG Group’s existing preferred stock and preferred securities (the amounts thereof included within Additional Tier 1 capital as of March 31, 2014 being ¥1,666.5 billion) and the Group’s existing subordinated debt issued before March 2013 (the amounts thereof included within Tier 2 capital as of March 31, 2014 being ¥1,349.6 billion) are subject to the phase-out arrangements.
	In November 2011, the Financial Stability Board announced policy measures to address systemically important financial institutions (“SIFIs”), which were endorsed by the G20 Leaders at the Cannes summit. The policy measures include requirements for globally systemically important banks (“G-SIBs”) to have additional loss absorption capacity tailored to the impact of their default, ranging from 1% to 2.5% of risk-weighted assets, to be met with Common Equity Tier 1 capital, which would be in addition to the 7.0% Common Equity Tier 1 capital requirement (including capital conservation buffer). The additional loss absorbency requirements will initially apply to G-SIBs identified in November 2014. The requirements will be phased in starting in January 2016 with full implementation by January 2019. Also in November 2011, the Financial Stability Board identified an initial group of G-SIFIs, namely 29 G-SIBs, including the MHFG Group, using a methodology developed by the Basel Committee on Banking Supervision, and announced that the group of G-SIFIs will be updated annually and published by the Financial Stability Board each November. In November 2012 and November 2013, the list of G-SIBs was updated and it showed the allocation to buckets corresponding to their required level of additional loss absorbency. The Group was included in the lists and was allocated to the bucket that would require 1.0% of additional loss absorbency.
	Regulatory adjustments are to be applied mainly to the calculation of Common Equity Tier 1 capital in the form of the deductions and prudential filters related to the following:
		•		Goodwill and other intangibles
		•		Deferred tax assets
		•		Deferred gains or losses on derivatives under hedge accounting that relates to the hedging of items that are not fair valued on the balance sheet
		•		Shortfall of the stock of provisions to expected losses under the internal ratings-based approach
		•		Gain on sale related to securitization transactions
		•		Cumulative gains and losses due to changes in own credit risk on fair valued financial liabilities
		•		Defined benefit pension fund assets and liabilities
		•		Treasury stock
		•		Reciprocal cross holdings of capital of banking, financial and insurance entities
		•		Investments in the capital of banking, financial and insurance entities that are outside the scope of regulatory consolidation
	Regulatory adjustments will be fully deducted in the calculation of Common Equity Tier 1 capital by March 2018. The regulatory adjustments began at 20% of the required deductions in the calculation of Common Equity Tier 1 capital in March 2014 and will be increased by 20% increments per year through March 2018 when the regulatory adjustments reach 100%. During this transition period, the remainder not deducted from capital will continue to be subject to existing national treatments.
	The capital requirements and regulatory adjustments will be phased in over a transitional period as follows (italicized percentages indicate those still in transition periods):
			March			March			March			March			March			March			March			March			March			March
			2013			2014			2015			2016			2017			2018			2019			2020			2021			2022
	Minimum Common Equity Tier 1 capital (Note)			3.5	%		4	%		4.5	%		4.5	%		4.5	%		4.5	%		4.5	%		4.5	%		4.5	%		4.5	%
	Minimum Tier 1 capital (Note)			4.5	%		5.5	%		6	%		6	%		6	%		6	%		6	%		6	%		6	%		6	%
	Minimum total capital (Note)			8	%		8	%		8	%		8	%		8	%		8	%		8	%		8	%		8	%		8	%
	Capital conservation buffer			0	%		0	%		0	%		0.625	%		1.25	%		1.875	%		2.5	%		2.5	%		2.5	%		2.5	%
	Phase out of recognition of capital instruments that no longer qualify as capital (Note)			90	%		80	%		70	%		60	%		50	%		40	%		30	%		20	%		10	%		0	%
	Phase-in of deductions from capital (Note)			0	%		20	%		40	%		60	%		80	%		100	%		100	%		100	%		100	%		100	%
	Additional loss absorbency requirements for G-SIBs			—			—			—			Additional loss absorption capacity tailored to the
													impact of the entity’s default, ranging from 1% to
													2.5% of risk-weighted assets, to be met with
													Common Equity Tier 1 capital
	Note:	While these measures are included in the revisions to capital adequacy guidelines that have been applied from March 31, 2013 as published by the Financial Services Agency, capital adequacy guidelines related to other requirements under the Basel III rules, such as the capital conservation buffer, countercyclical buffer and additional loss absorbency requirements for G-SIBs/G-SIFIs, have not yet been published.
	Japanese banks are also required to comply with the supervisory review process (second pillar) and disclosure requirements for market discipline (third pillar). Under the second pillar, banks are required to maintain adequate capital to support all of the major risks in their business and are encouraged to develop and use better risk management techniques in monitoring and managing such risks. Under the third pillar, banks are required to enhance disclosure, including disclosure of details of the capital adequacy ratio, the amount of each type of risk and the method of calculation used so that the market may make more effective evaluations. Further, the revisions to the Financial Services Agency’s guidelines relating to the third pillar, which reflect the enhanced disclosure requirements under Basel III and became effective on March 31, 2013, require banks to disclose, among other things, the components of their regulatory capital and the main features of their regulatory capital instruments in common templates.
	If the capital adequacy ratio of a financial institution falls below the required level, the Financial Services Agency may, depending upon the extent of capital deterioration, take certain corrective action, including requiring the financial institution to submit an improvement plan to strengthen its capital base, reduce its total assets, restrict its business operations or other actions that could have a material effect on its financial condition and results of operations.
	Capital adequacy ratios of MHFG, MHBK, and MHTB as of March 31, 2013 and 2014 calculated in accordance with Japanese GAAP and guidelines established by the Financial Services Agency are set forth in the following table:
			2013						2014
			Amount			Ratio			Amount			Ratio
			(in billions of yen, except percentages)
	Consolidated:
	MHFG:
	Common Equity Tier 1 capital:
	Required			2,059			3.5			2,411			4
	Actual			4,804			8.16			5,304			8.79
	Tier 1 capital:
	Required			2,647			4.5			3,316			5.5
	Actual			6,487			11.02			6,845			11.35
	Total risk-based capital:
	Required			4,706			8			4,823			8
	Actual			8,345			14.18			8,656			14.35
	MHBK (Note):
	Common Equity Tier 1 capital:
	Required			—			—			2,130			4
	Actual			—			—			5,387			10.11
	Tier 1 capital:
	Required			—			—			2,928			5.5
	Actual			—			—			6,525			12.25
	Total risk-based capital:
	Required			—			—			4,259			8
Actual			—			—			8,180			15.36
MHTB:
Common Equity Tier 1 capital:
Required			91			3.5			103			4
Actual			344			13.24			379			14.76
Tier 1 capital:
Required			117			4.5			141			5.5
Actual			344			13.24			379			14.76
Total risk-based capital:
Required			208			8			205			8
Actual			448			17.21			457			17.8
Non-consolidated:
MHBK (Note):
Common Equity Tier 1 capital:
Required			—			—			2,072			4
Actual			—			—			5,260			10.15
Tier 1 capital:
Required			—			—			2,849			5.5
Actual			—			—			6,370			12.29
Total risk-based capital:
Required			—			—			4,144			8
Actual			—			—			8,072			15.58
MHTB:
Common Equity Tier 1 capital:
Required			90			3.5			101			4
Actual			345			13.45			375			14.76
Tier 1 capital:
Required			115			4.5			139			5.5
Actual			345			13.45			375			14.76
Total risk-based capital:
Required			205			8			203			8
Actual			446			17.43			451			17.79
Note:	The former MHBK and the former MHCB merged on July 1, 2013 and the former MHCB, the surviving company, changed its trade name to MHBK.
Capital adequacy ratios of the former MHCB and the former MHBK as of March 31, 2013 are set forth in the following table:
		March 31, 2013
		Consolidated						Non-consolidated
		Amount			Ratio			Amount			Ratio
		(in billions of yen, except percentages)
The former MHCB (1):
Common Equity Tier 1 capital:
Required			1,292			3.5			1,143			3.5
Actual			3,195			8.65			2,993			9.16
Tier 1 capital:
Required			1,661			4.5			1,470			4.5
Actual			4,071			11.03			3,980			12.18
Total risk-based capital:
Required			2,953			8			2,613			8
Actual			5,130			13.89			5,008			15.33
The former MHBK (2) (3):
Common Equity Tier 1 capital:
Required			810			3.5			793			3.5
Actual			2,061			8.9			2,009			8.86
Tier 1 capital:
Required			1,041			4.5			1,020			4.5
Actual			2,344			10.13			2,252			9.93
Total risk-based capital:
Required			1,850			8			1,813			8
Actual			3,259			14.08			3,163			13.95
Notes:
-1	The distribution of all of the shares of MHSC to MHFG as a dividend in kind (¥424.4 billion) on April 1, 2013 was deducted from Common Equity Tier 1 capital.
-2	The amounts and ratios were calculated in accordance with Basel III and are included for reference purpose only because the former MHBK was subject to Basel II requirements as of March 31, 2013 as a financial institution without overseas operations to which only domestic capital adequacy requirements applied.
-3	The distribution of all of the shares of MHSC to MHFG as a dividend in kind (¥125.7 billion) on April 1, 2013 was deducted from Common Equity Tier 1 capital.
MHFG’s securities subsidiaries in Japan are also subject to the capital adequacy requirement under the Financial Instruments and Exchange Act. Under this requirement, securities firms must maintain a minimum capital adequacy ratio of 120% calculated as a percentage of capital accounts less certain assets, as determined in accordance with Japanese GAAP, against amounts equivalent to market, counterparty, and basic risks. Specific guidelines are issued as a ministerial ordinance that details the definition of essential components of the capital ratios, including capital, disallowed assets and risks, and related measures. Failure to maintain a minimum capital ratio will trigger mandatory regulatory actions. A capital ratio of less than 140% will call for regulatory reporting and a capital ratio of less than 100% may lead to a temporary suspension of all or part of the business operations and further, to the cancellation of the license to act as a securities broker and dealer.
Management believes, as of March 31, 2014, that MHFG, MHBK, MHTB, and their securities subsidiaries in Japan were in compliance with all capital adequacy requirements to which they were subject.
Business improvement orders
In September 2013, the Financial Services Agency issued a business improvement order to MHBK in connection with the transactions with anti-social elements in relation to a portion of certain joint loans. The business improvement order requires it to carry out promptly the measures to review, improve and reinforce the current structure of compliance and business administration thoroughly.
In December 2013, the Financial Services Agency issued business improvement orders to MHFG and MHBK with regard to the above mentioned transactions. The order to MHFG requires it to implement measures including clarification of where management responsibility lies based on the order and strengthening of its management control system. The order to MHBK requires it to cease new credit transactions under the four-party captive loan scheme for one month from January 20, 2014, as well as to implement the same measures as the order to MHFG.
The MHFG Group has been and will be rigidly implementing its improvement plans in relation to this problem and also work with utmost effort towards further improvement and reinforcement of its internal control systems.

Earnings_per_common_share

Earnings per common share	12 Months Ended
	Mar. 31, 2014
Earnings per common share	'
	18. Earnings per common share
	Basic earnings per common share are computed by dividing net income by the weighted average number of common shares outstanding during the fiscal year. Diluted earnings per common share reflect the assumed conversion to common shares of all convertible securities such as convertible preferred stock.
	The following table sets forth the computation of basic and diluted earnings per common share for the fiscal years ended March 31, 2012, 2013 and 2014:
			2012		2013		2014
			(in millions of yen)
	Net income:
	Net income attributable to MHFG shareholders			656,389		875,412		498,484
	Less: Net income attributable to preferred shareholders			8,672		8,221		6,745
	Net income attributable to common shareholders			647,717		867,191		491,739
	Effect of dilutive securities:
	Convertible preferred stock			7,571		7,121		6,437
	Net income attributable to common shareholders after assumed conversions			655,288		874,312		498,176
			2012		2013		2014
			(thousands of shares)
	Shares:
	Weighted average common shares outstanding			23,073,544		24,053,282		24,189,670
	Effect of dilutive securities:
	Convertible preferred stock (Note)			1,384,367		1,291,854		1,164,941
	Stock compensation-type stock options			11,628		20,093		16,641
	Weighted average common shares after assumed conversions			24,469,539		25,365,229		25,371,252
			2012		2013		2014
			(in yen)
	Amounts per common share:
	Basic net income per common share			28.07		36.05		20.33
	Diluted net income per common share			26.78		34.47		19.64
	Note:	The number of the dilutive common shares is based on the applicable conversion prices.

Income_taxes

Income taxes	12 Months Ended
	Mar. 31, 2014
Income taxes	'
	19. Income taxes
	The following table presents the components of Income tax expense for the fiscal years ended March 31, 2012, 2013 and 2014:
			2012			2013			2014
			(in millions of yen)
	Current:
	Domestic			22,103			37,101			92,814
	Foreign			32,714			10,754			42,919
	Total current tax expense			54,817			47,855			135,733
	Deferred:
	Domestic			(36,777	)		(40,021	)		94,911
	Foreign			(4,162	)		(3,810	)		(4,536	)
	Total deferred tax expense			(40,939	)		(43,831	)		90,375
	Total income tax expense			13,878			4,024			226,108
	The preceding table does not reflect the tax effects of items recorded directly in Equity for the fiscal years ended March 31, 2012, 2013 and 2014. The detailed amounts recorded directly in Equity are as follows:
			2012			2013			2014
			(in millions of yen)
	Unrealized net gains (losses) on available-for-sale securities:
	Unrealized gains (losses)			29,925			235,274			161,269
	Less: reclassification adjustments			18,249			(33,988	)		(70,228	)
	Total			48,174			201,286			91,041
	Pension liability adjustments:
	Unrealized gains (losses)			2,367			34,171			71,646
	Less: reclassification adjustments			8,992			5,913			2,442
	Total			11,359			40,084			74,088
	Total tax effect before allocation to noncontrolling interests			59,533			241,370			165,129
	The following table shows a reconciliation of Income tax expense at the effective statutory tax rate to the actual income tax expense for the fiscal years ended March 31, 2012, 2013 and 2014:
			2012			2013			2014
			(in millions of yen, except tax rates)
	Income before income tax expense (benefit)			662,835			885,180			726,343
	Effective statutory tax rate			40.69	%		38.01	%		38.01	%
	Income tax calculated at the statutory tax rate			269,708			336,457			276,083
	Income not subject to tax			(18,295	)		(18,320	)		(22,354	)
	Expenses not deductible for tax purposes			1,469			1,348			1,550
	Tax rate differentials of subsidiaries			(4,142	)		(10,535	)		(1,611	)
	Change in valuation allowance			(371,271	)		(1,352,597	)		(50,933	)
	Change in undistributed earnings of subsidiaries			(7,118	)		12,233			932
	Change in net operating loss carryforwards resulting from intercompany capital transactions			162			227			235
	Expiration of net operating loss carryforwards			33,576			1,026,439			6,313
	Effect of enacted change in tax rates			107,011	(1)		—			15,786	(2)
	Other			2,778			8,772			107
	Income tax expense (benefit)			13,878			4,024			226,108
	Notes:
	-1	On November 30, 2011, the National Diet of Japan approved two bills affecting the statutory tax rates of MHFG and its domestic subsidiaries. As a result, the statutory tax rate concerning MHFG’s tax returns for the fiscal years ended March 31, 2013 and 2014 has been reduced to 38.01% from the previous rate of 40.69%. Also, the rates for the fiscal year ending March 31, 2015 and for the fiscal years ending March 31, 2016 and thereafter will be 38.01% and 35.64%, respectively. The decrease of the Group’s balance of net deferred tax assets, reflecting such tax rate reductions, was recognized in Income tax expense in the fiscal year ended March 31, 2012.
	-2	On March 20, 2014, the National Diet of Japan approved a bill affecting the statutory tax rates of MHFG and its domestic subsidiaries. As a result, the statutory tax rate concerning MHFG’s tax returns for the fiscal year ending March 31, 2015 will be reduced to 35.64% from the previous rate of 38.01%. The decrease of the Group’s balance of net deferred tax assets, reflecting such tax rate reductions, was recognized in Income tax expense in the fiscal year ended March 31, 2014.
	The components of net deferred tax assets at March 31, 2013 and 2014 are as follows:
			2013			2014
			(in millions of yen)
	Deferred tax assets:
	Investments			889,305			724,038
	Allowance for loan losses			337,453			266,595
	Derivative financial instruments			—			29,002
	Trading account assets			—			19,842
	Net operating loss carryforwards			450,016			448,926
	Other			264,661			204,304
				1,941,435			1,692,707
	Valuation allowance			(584,665	)		(443,847	)
	Deferred tax assets, net of valuation allowance			1,356,770			1,248,860
	Deferred tax liabilities:
	Available-for-sale securities			567,608			659,448
	Prepaid pension cost and accrued pension liabilities			39,937			132,738
	Undistributed earnings of subsidiaries			11,040			11,972
	Premises and equipment			12,304			11,263
	Derivative financial instruments			35,391			—
Trading account assets			11,101			—
Other			51,913			61,500
Deferred tax liabilities			729,294			876,921
Net deferred tax assets			627,476			371,939
Deferred tax assets and deferred tax liabilities within the same tax jurisdiction have been netted for presentation purposes in the consolidated balance sheets.
In assessing the realizability of deferred tax assets, management considered whether it was more likely than not that some portion or all of the deferred tax assets would not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considered the scheduled reversal of deferred tax liabilities, projected future taxable income, and tax planning strategies available in making this assessment. Based upon the level of historical taxable income and projections for future taxable income over the periods in which the deferred tax assets would be deductible, management believed it was more likely than not that the MHFG Group would realize the benefits of these deductible differences, net of the existing valuation allowances at March 31, 2013 and 2014.
At March 31, 2014, the MHFG Group had net operating loss carryforwards totaling ¥1,414 billion. These carryforwards are scheduled to expire as follows:
		Net operating loss
		carryforwards
		(in billions of yen)
Fiscal year ending March 31:
2015			—
2016			—
2017			—
2018			865
2019			8
2020 and thereafter			541
Total			1,414
Included in net operating loss carryforwards in the above table are MHFG’s carryforwards of ¥868 billion resulting mainly from intercompany capital transactions. The tax effect of these carryforwards is offset by a full valuation allowance.
The total amount of unrecognized tax benefits including ¥802 million, ¥563 million and ¥699 million of interest and penalties was ¥2,160 million, ¥1,454 million and ¥1,691 million at March 31, 2012, 2013 and 2014, respectively, which would, if recognized, affect the Group’s effective tax rate. The Group classifies interest and penalties accrued relating to unrecognized tax benefits as Income tax expense.
The following table is a roll-forward of unrecognized tax benefits for the fiscal years ended March 31, 2012, 2013 and 2014:
		2012			2013			2014
		(in millions of yen)
Total unrecognized tax benefits at beginning of fiscal year			1,829			2,160			1,454
Gross amount of increases (decreases) related to positions taken during prior years			362			(471	)		(6	)
Gross amount of increases related to positions taken during the current year			244			29			100
Amount of decreases related to settlements			(227	)		(559	)		—
Foreign exchange translation			(48	)		295			143
Total unrecognized tax benefits at end of fiscal year			2,160			1,454			1,691
The MHFG Group is currently subject to ongoing tax audits in some jurisdictions. The oldest years open to tax audits in Japan, the United States and the United Kingdom are 2006, 2002 and 2002, respectively. The MHFG Group does not anticipate that increases or decreases of unrecognized tax benefits within the next twelve months would have a material effect on its consolidated results of operations or financial condition.

Pension_and_other_employee_ben

Pension and other employee benefit plans	12 Months Ended
	Mar. 31, 2014
Pension and other employee benefit plans	'
	20. Pension and other employee benefit plans
	Severance indemnities and pension plans
	MHFG and certain subsidiaries sponsor and offer their employees other than directors and corporate auditors, contributory and non-contributory defined benefit plans. Under these plans, employees are provided with lump-sum cash payments upon leaving the company. The amount of benefits under each plan is principally determined based on the position, the length of service and the reason for retirement. When employees meet certain conditions including the length of service, they may opt to receive annuity payments instead of lump-sum payments at retirement. MHFG and certain subsidiaries also offer special termination benefits to former employees whose contributions during their careers were deemed meritorious and to those with particular circumstances.
	Certain foreign offices and subsidiaries have defined contribution plans and/or defined benefit plans, of which disclosures are combined with those for domestic benefit plans, as they are not significant.
	MHFG and certain subsidiaries have several defined contribution plans. The costs recognized in respect of contributions to the plans for the fiscal years ended March 31, 2012, 2013 and 2014 were ¥2,129 million, ¥1,968 million and ¥2,487 million, respectively.
	Pension plans are not fully integrated among subsidiaries of MHFG and plan assets are managed separately by each plan.
	Net periodic benefit cost and funded status
	Net periodic benefit cost of the severance indemnities and pension plans for the fiscal years ended March 31, 2012, 2013 and 2014 includes the following components:
			2012			2013			2014
			(in millions of yen)
	Service cost-benefits earned during the fiscal year			27,734			30,422			33,429
	Interest costs on projected benefit obligation			24,267			23,186			20,341
	Expected return on plan assets			(28,234	)		(32,237	)		(37,047	)
	Amortization of prior service benefit			(318	)		(319	)		(195	)
	Amortization of net actuarial loss (gain)			25,595			16,936			7,039
	Special termination benefits (Note)			14,115			5,454			5,429
	Net periodic benefit cost			63,159			43,442			28,996
	Note:	The amount for the fiscal year ended March 31, 2012 includes special termination benefits of ¥9,828 million pertaining to MHSC’s voluntary retirement scheme.
	Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss) before-tax for the fiscal years ended March 31, 2013 and 2014 were summarized as follows:
			2013			2014
			(in millions of yen)
	Net actuarial gain (loss)			103,683			204,506
	Amortization of net actuarial loss (gain)			16,936			7,039
	Prior service benefit (cost)			(1,782	)		—
	Amortization of prior service benefit			(319	)		(195	)
	Total recognized in other comprehensive income (loss) before-tax			118,518			211,350
	As of March 31, 2014, the amounts in Accumulated other comprehensive income (loss), which will be amortized as prior service benefit and actuarial loss over the next fiscal year, are estimated to be ¥195 million and ¥137 million, respectively.
	Weighted-average assumptions used to determine benefit obligations and net periodic benefit cost are as follows:
			2012			2013			2014
	Weighted-average assumptions used to determine benefit obligations at fiscal year end:
	Discount rates			1.73	%		1.44	%		0.96	%
	Rates of increase in future compensation levels			2.33-6.46	%		2.31-6.57	%		2.00-4.80	%
	Weighted-average assumptions used to determine net periodic benefit cost during the year:
	Discount rates			1.83	%		1.73	%		1.44	%
	Rates of increase in future compensation levels			2.28-6.15	%		2.33-6.46	%		2.31-6.57	%
	Expected rates of return on plan assets			2.27	%		2.4	%		2.42	%
	In estimating the discount rates, the MHFG Group uses interest rates on high-quality fixed-income government and corporate bonds that received a rating of AA(Aa) or higher from rating agencies. The durations of such bonds closely match those of the benefit obligations. During the fiscal year ended March 31, 2014, the Group has changed the calculation method of the discount rates and has revised the benefit formula for some major plans to refine the estimate of benefit obligations. As a result of these refinements, total benefit obligations of the Group, at March 31, 2014, decreased by ¥110,744 million. Assumed discount rates are reevaluated at each measurement date. The expected rate of return for each asset category is based primarily on various aspects of the long-term prospects for the economy that include historical performance and the market environment.
	The following table sets forth the combined funded status and amounts recognized in the accompanying consolidated balance sheets at March 31, 2013 and 2014 for the plans of MHFG and its subsidiaries:
			2013			2014
			(in millions of yen)
	Change in benefit obligation:
	Benefit obligation at beginning of fiscal year			1,343,714			1,399,123
	Service cost			30,422			33,429
	Interest cost			23,186			20,341
	Plan participants’ contributions			1,184			1,181
	Amendments			1,782			—
	Actuarial loss (gain)			63,140			(70,214	)
	Foreign exchange translation			2,209			4,854
	Benefits paid			(49,593	)		(49,905	)
	Lump-sum payments			(16,921	)		(18,119	)
	Benefit obligation at end of fiscal year			1,399,123			1,320,690
	Change in plan assets:
	Fair value of plan assets at beginning of fiscal year			1,323,163			1,527,744
	Actual return (negative return) on plan assets			199,341			171,970
	Foreign exchange translation			1,783			4,128
	Employer contributions			51,866			50,936
	Plan participants’ contributions			1,184			1,181
	Benefits paid			(49,593	)		(49,905	)
	Fair value of plan assets at end of fiscal year			1,527,744			1,706,054
	Funded status			128,621			385,364
	Amounts recognized in the consolidated balance sheets consist of:
	Prepaid pension cost			153,414			403,654
	Accrued pension liability			(24,793	)		(18,290	)
Net amount recognized			128,621			385,364
Amounts recognized in Accumulated other comprehensive income (loss) before-tax consist of:
Prior service benefit (cost)			(440	)		(635	)
Net actuarial gain (loss)			(236,359	)		(24,814	)
Net amount recognized			(236,799	)		(25,449	)
Note:	The aggregated accumulated benefit obligations of these plans were ¥1,364,786 million and ¥1,319,771 million, respectively, as of March 31, 2013 and 2014. The defined benefit plans generally employ a multi-variable and non-linear formula based upon rank and years of service. Employees with service in excess of one year are qualified to receive lump-sum severance indemnities.
The following table shows the projected benefit obligations and the fair value of plan assets for the plans of MHFG and its subsidiaries with projected benefit obligations in excess of plan assets, and the accumulated benefit obligations and the fair value of plan assets for the plans with accumulated benefit obligations in excess of plan assets at March 31, 2013 and 2014:
		2013			2014
		(in millions of yen)
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligation			95,789			40,509
Fair value of plan assets			70,690			21,898
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligation			91,210			39,590
Fair value of plan assets			70,690			21,898
Note:	The plans with projected benefit obligations in excess of plan assets include those with accumulated benefit obligations in excess of plan assets.
Investment policies and asset allocation
In managing plan assets, the MHFG Group determines the appropriate levels of risk that the Group can assume under the given circumstances to maximize the investment returns from a long-term perspective while ensuring that the sufficient funds will be available to plan participants and beneficiaries. Generally, the investment returns are relative to the risks involved. In considering the maximum levels of risk that the MHFG Group can assume, it primarily considers the following factors; the employers’ burden of maintaining the benefit plans based on the design of the plans and future plan contributions, the age distribution of the plan participants and beneficiaries, the financial conditions of the employers, and the employers’ ability to absorb future variability in plan premiums. The long-term asset allocation to each asset category such as Japanese equity securities, Japanese debt securities, foreign equity securities and foreign debt securities is determined based upon the optimal portfolio, which is estimated to yield the maximum return within the range of acceptable level of risk. Additionally, the asset allocation is reviewed whenever there are large fluctuations in pension plan liabilities caused by modifications of pension plans, or there are changes in the market environment. When selecting an investment in each asset category, the MHFG Group takes into consideration credit standing of an investee, concentration of credit risk to a certain investee, liquidity of a financial instrument, etc. The investments in each asset category are further diversified across funds, strategies, sectors, etc. There is no significant investment in a single investee except Japanese government bonds.
Certain subsidiaries of MHFG established employee retirement benefit trusts and transferred their assets to the trusts as plan assets. These assets are separated from the employer’s proprietary assets for the payment to the plan beneficiaries. The assets held in these trusts are primarily Japanese equity securities and have been entrusted directly to qualified trustees including trust banks.
MHFG and certain subsidiaries’ target allocation for the plan assets excluding those of the employee retirement benefit trusts at March 31, 2014 is as follows:
Asset category		Asset ratio
Japanese equity securities			5	%
Japanese debt securities			44	%
Foreign equity securities			26	%
Foreign debt securities			10	%
General account of life insurance companies			14	%
Other			1	%
Total			100	%
Note:	General account of life insurance companies is a contract with life insurance companies which guarantees payments of principal and predetermined interest rate.
Fair value of plan assets
The following table presents the fair value of plan assets of MHFG and its subsidiaries at March 31, 2013 and 2014, by asset class. For the detailed information on fair value measurements, including descriptions of Level 1, 2 and 3 of the fair value hierarchy and the valuation methodologies, see Note 28 “Fair value”.
		2013											2014
		Level 1			Level 2			Level 3			Total		Level 1			Level 2			Level 3		Total
		(in billions of yen)
Japanese equity securities:
Common stocks (1)			716			—			—			716		782			—			—		782
Pooled funds (2)			—			86			—			86		5			51			—		56
Japanese debt securities:
Government bonds			179			—			—			179		229			—			—		229
Pooled funds (2)			—			46			—			46		—			68			—		68
Other			—			7			—			7		—			24			—		24
Foreign equity securities:
Common stocks			54			2			—			56		96			3			—		99
Pooled funds (2)			—			92			—			92		15			139			—		154
Foreign debt securities:
Government bonds			71			4			—			75		63			6			—		69
Pooled funds (2)			—			46			—			46		—			9			—		9
Other			—			23			—			23		—			15			—		15
General account of life insurance			—			111			—			111		—			111			—		111
companies (3)
Hedge funds			—			—			1			1		—			—			2		2
Other			92	(4)		(2	)(5)		—			90		91	(4)		(3	) (5)		—		88
Total assets at fair value			1,112			415			1			1,528		1,281			423			2		1,706
Notes:
-1	This class includes equity securities held in the employee retirement benefit trusts of ¥681 billion and ¥782 billion at March 31, 2013 and 2014, respectively, which are well-diversified across industries.
-2	These classes primarily include pension investment fund trusts. Investments in these classes are generally measured at their net asset values per share and can be redeemable within a short-term period upon request.
-3	Investments in this class are measured at conversion value.
-4	Amounts primarily include cash and short-term assets carried at fair value.
-5	Amounts primarily include foreign exchange contracts carried at fair value.
Amounts of actual returns on and purchases and sales of Level 3 assets during the fiscal years ended March 31, 2013 and 2014 were not significant.
Contributions
A contribution of approximately ¥49 billion is expected to be paid to the pension plans in the fiscal year ending March 31, 2015, based on the current funded status and expected asset return assumptions.
Estimated future benefit payments
The following table presents forecasted benefit payments including the effect of expected future service for the fiscal years indicated:
		(in millions of yen)
Fiscal year ending March 31:
2015			65,570
2016			68,183
2017			70,083
2018			71,558
2019			72,543
2020-2024			355,295

Stockbased_compensation

Stock-based compensation	12 Months Ended
	Mar. 31, 2014
Stock-based compensation	'
	21. Stock-based compensation
	Concurrently with the abolishment of, and as an alternative to the retirement allowances program for directors and executive officers of MHFG, the former MHBK, the former MHCB, and MHTB, the MHFG Group introduced stock compensation-type stock options, in the form of stock acquisition rights, for directors (excluding the outside directors) and executive officers of the respective companies (hereinafter referred to collectively as the “Directors”) in June 2008. The Group also introduced similar stock compensation-type stock options for MHSC’s Directors in June 2009. The Group maintained three types of stock-based compensation plans for Directors of MHFG, the former MHBK and the former MHCB (“MHFG Stock Plan”), for those of MHTB, and for those of MHSC. These three plans were integrated into MHFG Stock Plan during the fiscal year ended March 31, 2012, as MHTB and MHSC became MHFG’s wholly-owned subsidiaries and the stocks of these entities were delisted.
	MHFG Stock Plan
	In this plan, 1,000 shares of MHFG common stock shall be issued or transferred upon exercise of each of the stock acquisition rights. The amount to be paid upon exercise shall be 1 yen per share. The contractual term of the stock acquisition rights is 20 years. A holder may exercise the stock acquisition rights only after the date on which such holder loses the status as a Director of MHFG, MHBK, MHTB or MHSC.
	The following is a roll-forward of MHFG Stock Plan for the fiscal year ended March 31, 2014:
		Number of			Weighted-average			Weighted-average		Aggregate
		shares			exercise price			remaining		intrinsic value
								contractual term
					(in yen)			(in years)		(in millions of yen)
	Outstanding at beginning of fiscal year		23,863,000			1
	Granted during fiscal year		7,932,000			1
	Exercised during fiscal year		9,252,000			1
	Outstanding at end of fiscal year		22,543,000			1			18.47		4,576
	Exercisable at end of fiscal year		630,000			1			16.31		128
	There were no non-vested stock options remaining as of March 31, 2014.
	The following table presents the assumptions used in the Black-Scholes option pricing model to estimate the fair value of stock acquisition rights on the date of grant. The risk-free interest rate is based on the Japanese government bonds yield curve for the expected remaining term in effect at the date of grant. The expected volatility is based on the historical trading data of MHFG common stock. The expected remaining term is based on the average service period of Directors of MHFG, MHBK, MHTB and MHSC, which represents the period of time that stock acquisition rights granted are expected to be outstanding. The expected dividend yield is based on the dividend rate of MHFG common stock at the date of grant.
		For the stock acquisition rights granted
		during the fiscal years ended March 31,
		2013			2014
	Risk-free interest rate		0.1	%		0.08	%
	Expected volatility		29.3	%		28.16	%
	Expected remaining term (in years)		2.42			2.46
	Expected dividend yield		4.69	%		3.11	%
	The weighted-average grant-date fair value of stock acquisition rights granted during the fiscal years ended March 31, 2012, 2013 and 2014 was ¥91,840, ¥113,250 and ¥192,610, respectively.
	The compensation cost related to this plan recognized in income was ¥788 million, ¥1,333 million and ¥1,527 million during the fiscal years ended March 31, 2012, 2013 and 2014, respectively.

Derivative_financial_instrumen

Derivative financial instruments	12 Months Ended
	Mar. 31, 2014
Derivative financial instruments	'
	22. Derivative financial instruments
	The MHFG Group enter into derivative financial instruments in response to the diverse needs of customers, to control the risk related to the assets and liabilities of the MHFG Group, as part of its asset and liability management, and for proprietary trading purposes. The MHFG Group is exposed primarily to market risk associated with interest rate, commodity, foreign currency, and equity products. Market risk arises from changes in market prices or indices, interest rates and foreign exchange rates that may result in an adverse change in the market value of the financial instrument or an increase in its funding costs. Exposure to market risk is managed by imposing position limits and monitoring procedures and by initiating hedging transactions. In addition to market risk, the MHFG Group is exposed to credit risk associated with counterparty default or nonperformance in respect of transactions. Credit risk arises when a counterparty fails to perform according to the terms and conditions of the contract and the value of the underlying collateral held, if applicable, is not sufficient to recover resulting losses. The exposure to credit risk is measured by the fair value of all derivatives in a gain position and its potential increase at the balance sheet dates. The exposure to credit risk is managed by entering into legally enforceable master netting agreements to mitigate the overall counterparty credit risk, requiring underlying collateral and guarantees based on an individual credit analysis of each obligor and evaluating the credit features of each instrument. In addition, credit approvals, limits and monitoring procedures are also imposed.
	Notional amount and fair value of derivative contracts
	The following table summarizes the notional and fair value amounts of derivative instruments outstanding as of March 31, 2013 and 2014. The fair values of derivatives are presented on a gross basis and not offset against the right to reclaim cash collateral or the obligation to return cash collateral under master netting agreements in the consolidated balance sheets, or the table below.
						Fair value
						Derivative receivables (2)						Derivative payables (2)
	2013		Notional amount (1)			Designated			Not designated			Designated			Not designated
						as hedges			as hedges			as hedges			as hedges
			(in billions of yen)
	Interest rate contracts			854,698			—			10,350			—			10,018
	Foreign exchange contracts			118,708			—			3,099			10			2,973
	Equity-related contracts			3,419			—			182			—			177
	Credit-related contracts			5,266			—			59			—			44
	Other contracts			522			—			38			—			27
	Total			982,613			—			13,728			10			13,239
						Fair value
						Derivative receivables (2)						Derivative payables (2)
	2014		Notional amount (1)			Designated			Not designated			Designated			Not designated
						as hedges			as hedges			as hedges			as hedges
			(in billions of yen)
	Interest rate contracts			971,939			—			8,064			—			7,895
	Foreign exchange contracts			119,864			—			2,354			2			2,349
	Equity-related contracts			2,979			1			196			—			178
	Credit-related contracts			4,662			—			49			—			34
	Other contracts			463			—			23			—			17
	Total			1,099,907			1			10,686			2			10,473
	Notes:
	-1	Notional amount represents the sum of gross long and gross short third-party contracts.
	-2	Derivative receivables and payables are recorded in Trading account assets and Trading account liabilities, respectively.
	The MHFG Group provided and/or accepted cash collateral for derivative transactions under master netting agreements. The cash collateral, not offset against derivative positions, was included in Other assets and Other liabilities, respectively, of which the amounts were ¥742 billion and ¥503 billion at March 31, 2013, and ¥466 billion and ¥433 billion at March 31, 2014, respectively.
	Hedging activities
	In order to qualify for hedge accounting, a derivative must be considered highly effective at reducing the risk associated with the exposure being hedged. Each derivative must be designated as a hedge, with documentation of the risk management objective and strategy, including identification of the hedging instrument, the hedged item and the risk exposure, and how effectiveness is to be assessed prospectively and retrospectively. The extent to which a hedging instrument is effective at achieving offsetting changes in fair value or cash flows must be assessed at least quarterly. Any ineffectiveness must be reported immediately in earnings. The MHFG Group’s hedging activities include fair value and net investment hedges.
	Fair value hedges
	The MHFG Group primarily uses option and forward contracts to modify exposure to changes in fair value of available-for-sale securities. For qualifying fair value hedges, all changes in the fair value of the derivative and the corresponding hedged item relating to the risk being hedged are recognized in earnings in Investment gains (losses)—net. The change in fair value of the portion of the hedging instruments excluded from the assessment of hedge effectiveness is recorded in Trading account gains (losses)—net. No ineffectiveness exists because the MHFG Group chooses to exclude changes in the option’s time value and differences between the spot and the forward prices from the effectiveness test. If the hedge relationship is terminated, the fair value adjustment to the hedged item continues to be reported as part of the basis of the item and is amortized to earnings as a yield adjustment.
	The following table summarizes gains and losses information related to fair value hedges for the fiscal years ended March 31, 2012, 2013 and 2014:
			Gains (losses) recorded in income
	2012		Derivatives			Hedged			Hedge			Net gain (loss) excluded
						items			ineffectiveness			from assessment of
												effectiveness
			(in millions of yen)
	Interest rate contracts			(214	)		150			—			(64	)
	Equity-related contracts			(285	)		278			—			(7	)
	Total			(499	)		428			—			(71	)
			Gains (losses) recorded in income
	2013		Derivatives			Hedged			Hedge			Net gain (loss) excluded
						items			ineffectiveness			from assessment of
												effectiveness
			(in millions of yen)
	Interest rate contracts			44			(81	)		—			(37	)
	Equity-related contracts			352			(394	)		—			(42	)
	Total			396			(475	)		—			(79	)
			Gains (losses) recorded in income
	2014		Derivatives			Hedged			Hedge			Net gain (loss) excluded
						items			ineffectiveness			from assessment of
												effectiveness
			(in millions of yen)
	Equity-related contracts			801			(1,112	)		—			(311	)
	Total			801			(1,112	)		—			(311	)
	Net investment hedges
	The MHFG Group uses forward foreign exchange contracts and foreign currency-denominated debt instruments to protect the value of net investments in non-Japanese subsidiaries from foreign currency exposure. Under net investment hedges, both derivatives and nonderivative financial instruments qualify as hedging instruments. The foreign currency-denominated debt instruments qualifying as hedging instruments include deposits and long-term debt, of which the carrying amounts of the portion designated as net investment hedges are included within the respective items in the consolidated balance sheets as well as relevant accompanying notes. For net investment hedges, the changes in the fair value of a hedging derivative instrument or nonderivative hedging financial instrument is recorded in Foreign currency translation adjustments within Accumulated other comprehensive income (loss), provided that the hedging instrument is designated and is effective as a hedge of the net investment. The change in fair value of the ineffective portion is recorded in Foreign exchange gains (losses)—net in earnings. No amount is excluded from the assessment of hedge effectiveness of net investment hedges.
	The following table summarizes gains and losses information related to net investment hedges for the fiscal years ended March 31, 2012, 2013 and 2014:
			Gains (losses) recorded in income and other comprehensive income (“OCI”)
			2012						2013						2014
		Effective portion			Ineffective portion			Effective portion			Ineffective portion			Effective portion			Ineffective portion
		recorded in OCI			recorded in			recorded in OCI			recorded in			recorded in OCI			recorded in
					income						income						income
		(in millions of yen)
Financial instruments hedging foreign exchange risk			8,024			1,666			(65,851	)		(2,908	)		(102,150	)		(7,316	)
Total			8,024			1,666			(65,851	)		(2,908	)		(102,150	)		(7,316	)
Note:	Related to the effective portion of net investment hedges, Accumulated other comprehensive income of ¥1,893 million and ¥13,858 million were reclassified to earnings for the fiscal years ended March 31, 2012 and 2013 respectively. No amount related to the effective portion of net investment hedges was reclassified from Accumulated other comprehensive income (loss) to earnings for the fiscal year ended March 31, 2014.
Derivative instruments not designated or qualifying as hedges
The MHFG Group enters into the following derivative transactions that do not qualify for hedge accounting with a view to implementing risk management hedging strategies: (1) interest-rate swap transactions for the purpose of hedging interest-rate risks in deposits, loans etc., (2) currency swap transactions for the purpose of hedging the foreign exchange risk of these assets, and (3) credit derivatives for the purpose of hedging the credit risk in loans, RMBS, CMBS, CLO and other similar assets. Such derivatives are accounted for as trading positions. The changes in fair value of these instruments are primarily recorded in Trading account gains (losses)—net, even though they are used to mitigate or transform the risk of exposures arising from banking activities. The net gain (loss) resulting from changes in the fair value of certain credit derivatives where the Group purchases protection to mitigate its credit risk exposure, related to its corporate loan portfolio, is recorded in Other noninterest income (expenses).
The following table summarizes gains and losses on derivatives not designated or qualifying as hedges during the fiscal years ended March 31, 2012, 2013 and 2014:
		Gains (losses) recorded in income
		2012			2013			2014
		(in millions of yen)
Interest rate contracts (1)			261,632			219,422			(79,562	)
Foreign exchange contracts			(146,258	)		(91,300	)		(13,167	)
Equity-related contracts (1)			(7,143	)		(59,421	)		(41,296	)
Credit-related contracts (2)			(5,575	)		(6,877	)		(7,761	)
Other contracts			283			(2,378	)		(6,857	)
Total			102,939			59,446			(148,643	)
Notes:
-1	The net gain (loss) excluded from the assessment of the effectiveness of fair value hedges is not included in the above table.
-2	Amounts include the net loss of ¥3,391 million, ¥6,703 million and ¥8,660 million on the credit derivatives hedging the credit risk of loans during the fiscal years ended March 31, 2012, 2013 and 2014, respectively.
Credit derivatives
A credit derivative is a bilateral contract between a seller and a buyer of protection against the credit risk of a particular entity. Credit derivatives generally require that the seller of credit protection make payments to the buyer upon the occurrence of predefined credit events, which include bankruptcy, dissolution or insolvency of the referenced entity. The MHFG Group either purchases or writes protection on either a single name or a portfolio of reference credits. The Group enters into credit derivatives to help mitigate credit risk in its corporate loan portfolio and other cash positions, to take proprietary trading positions, and to facilitate client transactions.
The notional amount of credit derivatives represents the maximum potential amount of future payments the seller could be required to make. If the predefined credit event occurs, the seller will generally have a right to collect on the underlying reference credit and any related cash flows, while being liable for the full notional amount of credit protection to the buyer. The Group manages credit risk associated with written protection by purchasing protection with identical or similar underlying reference credits, which substantially offsets its exposure. Thus, the notional amount is not necessarily a reliable indicator of the Group’s actual loss exposure.
The following table summarizes the notional and fair value amounts of credit derivatives at March 31, 2013 and 2014:
		2013						2014
		Notional amount			Fair value			Notional amount			Fair value
		(in billions of yen)
Credit protection written:
Investment grade			1,810			1			1,723			21
Non-investment grade			652			1			479			3
Total			2,462			2			2,202			24
Credit protection purchased			2,870			13			2,548			(9	)
Note:	The rating scale is based upon either the external ratings or the internal ratings of the underlying reference credit. The lowest investment grade rating is considered to be BBB- or the corresponding internal rating, while anything below or unrated is considered to be non-investment grade. Non-investment grade credit derivatives primarily consist of unrated credit default swap indices such as CDX and iTraxx.
The following table shows the maximum potential amount of future payments for credit protection written by expiration period at March 31, 2013 and 2014:
		Maximum payout/Notional amount
		2013			2014
		(in billions of yen)
One year or less			620			325
After one year through five years			1,720			1,791
After five years			122			86
Total			2,462			2,202
Note:	The maximum potential amount of future payments is the aggregate notional amount of the credit derivatives where the Group wrote the credit protection, and it has not been reduced by the Group’s right of collection over the underlying assets and the related cash flows, nor netted against that of credit protection purchased.
Credit-related contingent features
Certain of the MHFG Group’s derivative instruments contain provisions that require the Group’s debt to maintain an investment grade credit rating from the major credit rating agencies. If the Group’s debt credit rating were to fall below investment grade, the counterparties to the derivative instruments could request immediate payment or demand immediate and ongoing full overnight collateralization on derivative instruments which are in net liability positions for the Group. The aggregate fair value of all derivative instruments with such credit-risk-related contingent features in net liability positions on March 31, 2013 and 2014 was ¥1,022 billion and ¥687 billion, respectively. As the Group has provided ¥1,029 billion and ¥614 billion as collateral to the counterparties in the normal course of its business on March 31, 2013 and 2014, respectively, if the contingent features described above were triggered on March 31, 2013 and 2014, there was no amount that the Group would be required to post as collateral or settle immediately on March 31, 2013, while the amount required to be posted as collateral or settled immediately would be ¥73 billion on March 31, 2014.

Commitments_and_contingencies

Commitments and contingencies	12 Months Ended
	Mar. 31, 2014
Commitments and contingencies	'
	23. Commitments and contingencies
	Obligations under guarantees
	The MHFG Group provides guarantees or indemnifications to counterparties to enhance their credit standing and enable them to complete a variety of business transactions. A guarantee represents an obligation to make payments to third parties if the counterparty fails to fulfill its obligation under a borrowing arrangement or other contractual obligation.
	The types of guarantees under ASC 460, “Guarantees” (“ASC 460”) provided by the MHFG Group are described below.
	Performance guarantees
	Performance guarantees are issued to guarantee customers’ performance under contractual arrangements such as a tender bid on a construction project or the completion of a construction project.
	Guarantees on loans
	Guarantees on loans include obligations to guarantee the customers’ borrowing contracts. The MHFG Group is required to make payments to the guaranteed parties in the event that customers fail to fulfill obligations under the contracts.
	Guarantees on securities
	Guarantees on securities include obligations to guarantee securities, such as bonds issued by customers.
	Other guarantees
	Other guarantees include obligations to guarantee customers’ payments, such as tax payments.
	Guarantees for the repayment of trust principal
	The MHFG Group provides certain trust products with guarantees for the repayment of trust principal, e.g., loan trusts and certain jointly operated designated money trusts. Pursuant to Japanese trust-related laws, trustees are prohibited from compensating beneficiaries for any loss in the beneficial interests in each trust. However, under a special condition of the Japanese trust-related laws, trust banks as trustees are allowed to enter into an agreement to provide compensation for any loss in the principal of the trust. The MHFG Group manages and administers the trust assets to minimize exposures against losses from the guarantees for the repayment of trust principal, including writing-off impaired loans and charging it to the trust account profits. In performing its fiduciary duties, the MHFG Group also manages the trust assets separately from its own proprietary assets on behalf of customers and keeps separate records for the trust activities. The MHFG Group consolidates certain guaranteed principal money trusts. See Note 25 “Variable interest entities and securitizations” for further discussion of the guaranteed principal money trust. The contract amounts of guarantees for repayment of unconsolidated trust principal are presented in the tables below.
	Part of the trust account profits is set aside as a reserve in trust accounts to absorb losses in the trust asset portfolios in accordance with relevant Japanese laws concerning the trust business and/or trust agreements. Statutory reserves for loan trusts and reserves for jointly operated designated money trusts are calculated based on the trust principal or the balance of loans and other assets in the trust accounts. Since the probability of principal indemnification is judged to be remote, the MHFG Group had no related reserve for credit losses recorded in its consolidated financial statements.
	Liabilities of trust accounts
	The MHFG Group, as trustee, may enter into an agreement with a third party who is not the party to the relevant trust agreement to the extent necessary to handle the trust affairs for the purpose of fulfilling the objectives of the trust and, as such, the trustee shall be allowed to assume certain liabilities. Pursuant to Japanese trust-related laws, the trustee is ultimately liable to pay those liabilities out of its proprietary assets in the event that the trust assets are insufficient to cover those liabilities. The amount of trust liabilities rarely exceeds the amount of trust assets and, therefore, those liabilities are generally covered by the corresponding trust assets. To avoid the demand for payment out of the proprietary assets, the trustee can enter into a special covenant of limited liability under which the trust creditors agree to limit the trustee’s liability to the value of the trust assets and to waive the right for compulsory execution against the trustee’s proprietary assets. The MHFG Group regularly monitors the condition of trust accounts to minimize exposures against making payment.
	The amounts of such liabilities in the trust accounts, excluding those with the special covenant of limited liability, are presented in the tables below. Liabilities of trust accounts principally include obligations to return collateral under security lending transactions and other transactions.
	Derivative financial instruments
	Certain written options and credit default swaps are deemed guarantees pursuant to the definition of guarantees in ASC 460 if these contracts require the MHFG Group to make payments to counterparties based on changes in an underlying instrument or index that is related to an asset, a liability, or an equity security of the counterparties. The MHFG Group’s payments could involve a gross settlement or a net settlement. Because it is difficult in practice to determine whether the counterparty has the asset, the liability or the equity security relating to the underlying, the MHFG Group has decided to include all credit default swaps and written options, excluding written options outside the scope of ASC 460, in the guarantee disclosures.
	Carrying amount
	The MHFG Group records all guarantees and similar obligations subject to ASC 460 at fair value on the consolidated balance sheets at the inception of the guarantee. The total carrying amount of guarantees and similar obligations at March 31, 2013 and 2014 was ¥512 billion and ¥ 422 billion, respectively, and was included in Other liabilities and Trading account liabilities. The total includes the carrying amounts of derivatives that are deemed to be guarantees, which amounted to ¥493 billion and ¥404 billion at March 31, 2013 and 2014, respectively.
	Maximum exposure under guarantee contracts
	The table below summarizes the remaining term and maximum potential amount of future payments by type of guarantee at March 31, 2013 and 2014. The maximum potential amount of future payments disclosed below represents the contractual amounts that could be repaid in the event of the guarantees being executed, without consideration of possible recoveries under recourse provisions or from collateral held. With respect to written options included in derivative financial instruments in the table below, in theory, the MHFG Group is exposed to unlimited losses; therefore, the table shows the notional amounts of the contracts as a substitute for the maximum exposure.
	The MHFG Group, when necessary, requires collateral such as cash, investment securities and real estate or third-party guarantees depending on the amount of credit risk involved, and employs means such as sub-participation to reduce the credit risk associated with guarantees. The maximum exposure or notional amount below does not represent the expected losses from the execution of the guarantees.
	2013		Maximum		Amount by expiration period
			potential/Contractual
			or Notional amount		One year or less		After one year		After five years
							through
							five years
			(in billions of yen)
	Performance guarantees			1,750		935		619		196
	Guarantees on loans			452		159		51		242
	Guarantees on securities			146		19		127		—
	Other guarantees			1,068		826		217		25
	Guarantees for the repayment of trust principal			171		—		133		38
	Liabilities of trust accounts			8,606		8,428		72		106
	Derivative financial instruments			23,582		10,185		11,837		1,560
	2014		Maximum		Amount by expiration period
			potential/Contractual
			or Notional amount		One year or less		After one year		After five years
							through
							five years
			(in billions of yen)
	Performance guarantees			1,985		1,125		708		152
	Guarantees on loans			399		173		21		205
	Guarantees on securities			170		42		128		—
	Other guarantees			1,249		991		220		38
	Guarantees for the repayment of trust principal			158		—		125		33
	Liabilities of trust accounts			11,158		10,962		78		118
	Derivative financial instruments			21,422		8,643		11,391		1,388
	The table below presents the maximum potential amount of future payments of performance guarantees, guarantees on loans, guarantees on securities and other guarantees classified based on internal ratings at March 31, 2013 and 2014:
			2013		2014
			(in billions of yen)
	Investment grade			2,387		2,673
	Non-investment grade			1,029		1,130
	Total			3,416		3,803
	Note:	Investment grade in the internal rating scale generally corresponds to BBB- or above in external rating scale.
	Other off-balance-sheet instruments
	In addition to guarantees, the MHFG Group issues other off-balance-sheet instruments to its customers, such as lending-related commitments and commercial letters of credit. Under the terms of these arrangements, the MHFG Group is required to extend credit or make certain payments upon the customers’ request.
	Commitments to extend credit
	Commitments to extend credit are legally binding agreements to lend to customers on demand. They usually have set maturity dates. These agreements differ from guarantees in that they are generally revocable or contain provisions that enable the MHFG Group to avoid payment or reduce the amount of credit extended under certain conditions, such as the deterioration of the borrower’s financial condition or other reasonable conditions. The MHFG Group monitors the financial condition of the potential borrowers throughout the commitment period to determine whether additional collateral or changes in the terms of the commitment are necessary. Since many of these commitments to extend credit expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements.
	Commitments to invest in securities
Commitments to invest in securities include legally binding contracts to make additional contributions to investment funds, such as venture capital funds or corporate recovery funds in accordance with the terms of investment agreements.
Commercial letters of credit
Commercial letters of credit are issued in connection with customers’ trade transactions. Normally, the customers cannot receive the goods until they make payment to a bank, and therefore these commercial letters of credit are collateralized by the underlying goods. Upon issuance of commercial letters of credit, the MHFG Group monitors the credit risk associated with these transactions to determine if additional collateral is required.
The table below summarizes the contractual amounts with regard to these undrawn commitments at March 31, 2013 and 2014:
		2013		2014
		(in billions of yen)
Commitments to extend credit (Note)			59,101		59,402
Commercial letters of credit			608		611
Total			59,709		60,013
Note: Commitments to extend credit include commitments to invest in securities.
Allowance for losses on off-balance-sheet instruments
The amounts of an allowance for losses on off-balance-sheet instruments at March 31, 2013 and 2014 were ¥102 billion and ¥121 billion, respectively.
Leases
The MHFG Group leases certain office space and equipment under noncancelable agreements. The lease periods for these leases range from less than 1 year to around 30 years. These leases include cancellation clauses with penalties of a maximum of approximately 5 years-worth of rentals and/or periodic adjustment clauses of rentals. Future minimum lease payments for capitalized leases and future minimum rental payments for operating leases at March 31, 2014 were as follows:
		Capitalized leases		Operating leases
		(in millions of yen)
Fiscal year ending March 31:
2015			6,479		48,233
2016			5,929		40,195
2017			5,186		35,584
2018			4,547		31,556
2019			3,820		29,237
2020 and thereafter			2,068		74,596
Total minimum lease/rental payments			28,029		259,401
Amount representing interest			1,349
Present value of minimum lease payments			26,680
Total rental expense for the fiscal years ended March 31, 2012, 2013 and 2014 was ¥101,003 million, ¥98,459 million and ¥95,941 million, respectively.
During prior years, the MHFG Group’s major banking subsidiaries sold their head offices (including land, buildings, facilities and equipment) to third parties. Concurrent with the sales, these subsidiaries leased the properties back for periods of 5 and 10 years for total rental payments for these periods of ¥214,690 million. The terms of certain lease agreements were changed during the fiscal years ended March 31, 2009, 2011, 2012 and 2014, and the total rental payments for these periods increased to ¥282,832 million, consequently. The MHFG Group accounted for the transactions as operating leases. The future minimum rental payments under the terms of the related lease agreements were ¥29,879 million, ¥15,907 million and ¥69,556 million at March 31, 2012, 2013 and 2014, respectively.
During the fiscal year ended March 31, 2014, MHFG began to lease its head office from a third party and accounted for the lease arrangement as operating lease.
Legal proceedings
The MHFG Group is involved in normal collection proceedings initiated by the Group and other legal proceedings in the ordinary course of business.
The Group’s Indonesian subsidiary acts as collateral agent for the trustee of bond issuances made by subsidiaries of Asia Pulp & Paper Company Ltd. (“APP”). In that role, the subsidiary is involved in a dispute between the bondholders and such APP subsidiaries in their capacities as the issuers, guarantors and/or pledgors of security for the bonds relating to foreclosure proceedings on the collateral and has been named as a defendant in a lawsuit brought by the obligors under the bonds in Indonesia. The Group’s consolidated financial statements do not include a reserve in relation to this dispute because the Group does not believe that the resolution of this matter will have a significant impact on the consolidated financial condition or results of operations of the Group, although there can be no assurance as to the foregoing.

Noncontrolling_interests_in_co

Noncontrolling interests in consolidated subsidiaries	12 Months Ended
	Mar. 31, 2014
Noncontrolling interests in consolidated subsidiaries	'
	24. Noncontrolling interests in consolidated subsidiaries
	Noncontrolling interests represent the equity of the remaining outstanding voting stock of subsidiaries not owned by the MHFG Group. The changes in the noncontrolling interests in fiscal years ended March 31, 2012, 2013 and 2014 consisted of noncontrolling interests in the net income or loss of subsidiaries, noncontrolling interests in changes in other comprehensive income of subsidiaries and changes in the ownership percentage of the Group in respect of certain subsidiaries.
	During the fiscal year ended March 31, 2012, the MHFG Group exchanged certain MHFG’s common stock for 30.15, 40.80 and 46.02 percent of the voting equity interests in MHTB, the former MHSC and the former MHIS, respectively, in order for those subsidiaries to become MHFG’s wholly-owned subsidiaries. See Note 14 “Common stock” for further details of these transactions. Subsequently, the Group transferred 5.34 percent of the voting equity interests in the former MHSC to The Norinchukin Bank.

Variable_interest_entities_and

Variable interest entities and securitizations	12 Months Ended
	Mar. 31, 2014
Variable interest entities and securitizations	'
	25. Variable interest entities and securitizations
	Variable interest entities
	In the normal course of business, the MHFG Group is involved with VIEs primarily through the following types of transactions: asset-backed commercial paper/loan programs, asset-backed securitizations, investments in securitization products, investment funds, trust arrangements, and structured finance. The Group consolidates certain of these VIEs, where the Group is deemed to be the primary beneficiary because it has both (1) the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and (2) the obligation to absorb losses or the right to receive benefits that could potentially be significant to the VIE. The MHFG Group reassesses whether it is primary beneficiary on an ongoing basis as long as the Group has any continuing involvement with the VIE. There are also other VIEs, where the Group determines that it is not the primary beneficiary but has significant variable interests. In evaluating the significance of the variable interests, the Group comprehensively takes into consideration the extent of its involvement with each VIE, such as the seniority of its investments, the share of its holding in each tranche and the variability it expects to absorb, as well as other relevant facts and circumstances. The likelihood of loss is not necessarily relevant to the determination of significance, and therefore, “significant” does not imply that there is high likelihood of loss. The maximum exposure to loss that is discussed in this section refers to the maximum loss that the Group could be required to record in its consolidated statements of income as a result of its involvement with the VIE. This represents exposures associated with both on-balance-sheet assets and off-balance-sheet liabilities related to the VIE. Further, this maximum potential loss is disclosed regardless of the probability of such losses and, therefore, it is not indicative of the ongoing exposure which is managed within the Group’s risk management framework.
	The tables below show consolidated assets of the Group’s consolidated VIEs as well as total assets and maximum exposure to loss for its significant unconsolidated VIEs, as of March 31, 2013 and 2014:
		Consolidated VIEs		Significant
				unconsolidated VIEs
	2013	Consolidated assets		Total assets		Maximum
						exposure to loss
		(in billions of yen)
	Asset-backed commercial paper/loan programs		2,212		—		—
	Asset-backed securitizations		385		463		37
	Investments in securitization products		—		530		206
	Investment funds		1,175		2,770		302
	Trust arrangements and other		39		—		—
	Total		3,811		3,763		545
		Consolidated VIEs		Significant
				unconsolidated VIEs
	2014	Consolidated assets		Total assets		Maximum
						exposure to loss
		(in billions of yen)
	Asset-backed commercial paper/loan programs		2,403		—		—
	Asset-backed securitizations		423		385		39
	Investments in securitization products		181		531		200
	Investment funds		1,508		2,935		387
	Trust arrangements and other		38		—		—
	Total		4,553		3,851		626
	The Group has not provided financial or other support to consolidated or unconsolidated VIEs that the Group was not previously contractually required to provide.
	The tables below present the carrying amounts and classification of assets and liabilities on the MHFG Group’s balance sheets that relate to its variable interests in the significant unconsolidated VIEs, as of March 31, 2013 and 2014:
	Assets on balance sheets related to unconsolidated VIEs:	2013		2014
		(in billions of yen)
	Trading account assets		46		29
	Investments		206		222
	Loans		308		316
	Total		560		567
	Liabilities on balance sheets and maximum exposure to loss related to unconsolidated VIEs:	2013		2014
		(in billions of yen)
	Payables under securities lending transactions		14		4
	Total		14		4
	Maximum exposure to loss		545		626
	Asset-backed commercial paper/loan programs
	The MHFG Group manages several asset-backed commercial paper/loan programs that provide its clients’ off-balance-sheet and/or cost-effective financing. The VIEs used in the programs purchase financial assets, primarily receivables, from clients participating in the programs and provide liquidity through the issuance of commercial paper or borrowings from the MHFG Group backed by the financial assets. While customers normally continue to service the transferred receivables, the MHFG Group underwrites, distributes, and makes a market in commercial paper issued by the conduits. The MHFG Group typically provides program-wide liquidity and credit support facilities and, in some instances, financing to the VIEs. The MHFG Group has the power to determine which assets will be held in the VIEs and has an obligation to monitor these assets. The Group is also responsible for liability management. In addition, through the liquidity and credit support facilities with the VIEs, the Group has the obligation to absorb losses that could potentially be significant to the VIEs. Therefore, the Group consolidates this type of VIEs.
	Asset-backed securitizations
	The MHFG Group acts as an arranger of various types of structured finance to meet clients’ off-balance-sheet financing needs. In substantially all of these structured financing transactions, the transfer of the financial asset by the client is structured to be bankruptcy remote by use of a bankruptcy remote entity, which is deemed to be a VIE because its equity holder does not have decision making rights. The MHFG Group receives fees for structuring and/or distributing the securities sold to investors. In some cases, the MHFG Group itself purchases the securities issued by the entities and/or provides loans to the VIEs.
	In addition, the MHFG Group establishes several single-issue and multi-issue special purpose entities that issue collateralized debt obligations (“CDO”) or CLO, synthetic CDO/CLO or other repackaged instruments to meet clients’ and investors’ financial needs. The MHFG Group also arranges securitization transactions including CMBS, RMBS and others. In these transactions, the MHFG Group acts as an underwriter, placement agent, asset manager, derivatives counterparty, and/or investor to debt and equity instruments.
	In certain VIEs, where the MHFG Group provides liquidity and credit support facilities, writes credit protection or invests in debt or equity instruments in its role as an arranger, servicer, administrator or asset manager, etc., the Group has the power to determine which assets will be held in the VIEs or to manage and monitor these assets. In addition, through the variable interests above, the Group has the obligation to absorb losses and the right to receive benefits that could potentially be significant to the VIEs. Therefore, the Group consolidates such VIEs.
	The MHFG Group established certain VIEs to securitize its own mortgage loans. The Group provides servicing for, holds retained subordinated beneficial interests in, and retains credit exposure in the form of guarantees in the mortgage loans. In its role as a servicer, the Group has the power to direct the entity’s activities that most significantly impact the entity’s economic performance by managing defaulted mortgage loans. In addition, through the retained interests and the involvement as a guarantor above, the Group has the obligation to absorb losses and the right to receive benefits that could potentially be significant to the entity. Therefore, the Group consolidates such VIEs.
	Investments in securitization products
	The MHFG Group invests in, among other things, various types of CDO/CLO, synthetic CDO/CLO and repackaged instruments, CMBS and RMBS arranged by third parties for the purpose of generating current income or capital appreciation, which all utilize entities that are deemed to be VIEs. By design, such investments were investment grade at issuance and held by a diverse group of investors. The potential loss amount of securities and loans is generally limited to the amount invested because the Group has no contractual involvement in such VIEs beyond its investments. Since the Group is involved in those VIEs only as an investor, the Group does not ordinarily have the power to direct the VIEs’ activities that most significantly impact the VIEs’ economic performance. However, the Group consolidates VIEs, where the transactions are tailored by the third party arrangers to meet the Group’s needs as a main investor, who is ultimately deemed to have the power to determine which assets to be held in the VIEs. The Group also invests in certain beneficial interests issued by VIEs which hold real estate that the Group utilizes. In addition to these variable interests, when the Group has the power including the sole unilateral ability to liquidate VIEs, the Group consolidates such VIEs.
	Investment funds
	The MHFG Group invests in various investment funds including securities investment trusts, which collectively invest in equity and debt securities that include listed Japanese securities and investment grade bonds. Investment advisory companies or fund management companies, including the Group’s subsidiaries and affiliates, administer and make investment decisions over such investment funds. The Group consolidates certain investment funds where it is deemed to be the primary beneficiary. The Group has determined that certain investment vehicles managed by the Group that have all the attributes of an investment company (or similar entity) qualify for the deferral from certain requirements of ASC 810 that originated from SFAS No.167 “Amendments to FASB Interpretation No. 46(R)” (“SFAS No. 167”). Therefore, for these vehicles, the Group determines whether it is the primary beneficiary by evaluating whether it absorbs a majority of expected losses, receives a majority of expected residual returns, or both.
	Trust arrangements
	The MHFG Group offers a variety of asset management and administration services under trust arrangements including security investment trusts, pension trusts and trusts used in the securitization of assets originated by and transferred to third parties. The Group receives trust fees for providing services as an agent or fiduciary on behalf of beneficiaries.
	With respect to guaranteed principal money trust products, the MHFG Group assumes certain risks by providing guarantees for the repayment of principal as required by the trust agreements or relevant Japanese legislation. The MHFG Group manages entrusted funds primarily through the origination of high quality loans and other credit-related products, investing in investment grade marketable securities such as Japanese government bonds and placing cash with the MHFG Group’s subsidiary trust banks. The Group has the power to determine which assets will be held in the VIEs or to manage these assets. In addition, through the principal guarantee agreement, the Group has the obligation to absorb losses that could potentially be significant to the VIEs. Therefore, the Group consolidates this type of VIEs. However, the MHFG Group does not consolidate certain guaranteed principal money trusts, which invest all the entrusted funds in the MHFG Group itself, as the Group has determined that it has no variable interests (Refer to Note 10 “Due to trust accounts”). See Note 23 “Commitments and contingencies” for the balances of guaranteed trust principal unconsolidated at March 31, 2013 and 2014.
	With respect to non-guaranteed trust arrangements, the MHFG Group manages and administers assets on behalf of its customers (trust beneficiaries) in the capacity of a trustee and fiduciary. For substantially all non-guaranteed trust arrangements, the Group generally does not have the power to direct the activities of the VIEs that most significantly impact the VIEs’ economic performance or has neither the obligation to absorb losses nor the right to receive benefits that could potentially be significant to the VIEs. Therefore, such trust accounts are not included in the consolidated financial statements of the MHFG Group.
	The Group has determined that, in certain trust arrangements that have all the attributes of an investment company (or similar entity), certain requirements of ASC 810 that originated from SFAS No.167 are deferred. Therefore, for these trust arrangements, the Group determines whether it is the primary beneficiary by evaluating whether it absorbs a majority of expected losses, receives a majority of expected residual returns, or both.
	Special purpose entities created for structured finance
	The MHFG Group is involved in real estate, commercial aircraft and other vessel and machinery and equipment financing to VIEs. As the Group typically only provides senior financing with credit enhanced by subordinated interests and sometimes may act as an interest rate swap counterparty, the Group determines that, in this type of VIEs, it does not have the power to direct the activities of the VIEs that most significantly impact the VIEs’ economic performance, or even the significant variable interests.
	Securitization
	The MHFG Group has had no significant transfers of financial assets, recognized no significant gains or losses and retained no significant interests in securitization transactions accounted for as sales.
	There are certain transactions where transfers of financial assets do not qualify for sale treatment but are accounted for as secured borrowings. These transferred assets continue to be carried on the consolidated balance sheets of the MHFG Group. Such assets are associated with securitization transactions and loan participation transactions, which amounted to ¥174 billion and ¥62 billion as of March 31, 2013, and ¥181 billion and ¥79 billion as of March 31, 2014, respectively. Liabilities associated with securitization and loan participation transactions are presented as Payables under securities lending transactions and Other short-term borrowings or Long-term debt, respectively, on the consolidated balance sheets.

Fees_and_commissions_income

Fees and commissions income	12 Months Ended
	Mar. 31, 2014
Fees and commissions income	'
	26. Fees and commissions income
	Details of Fees and commissions income for the fiscal years ended March 31, 2012, 2013 and 2014 are as follows:
		2012		2013		2014
		(in millions of yen)
	Securities-related business		116,567		132,787		170,311
	Deposits, debentures and lending business		97,509		113,989		114,073
	Remittance business		105,015		104,574		108,534
	Trust fees		45,990		45,621		48,914
	Fees for other customer services		210,332		215,837		233,931
	Total		575,413		612,808		675,763
	Securities-related business fees consist of broker’s fees and markups on securities underwriting and other securities related activities. Remittance business fees consist of service charges for funds transfer and collections. Trust fees are earned primarily by fiduciary asset management and administration service for corporate pension plans, investment funds, and other. Fees for other customer services include fees related to the MHFG Group’s agency business, guarantee related business, and other.

Trading_account_gains_and_loss

Trading account gains and losses	12 Months Ended
	Mar. 31, 2014
Trading account gains and losses	'
	27. Trading account gains and losses
	The MHFG Group performs trading activities through market making, sales, and arbitrage. Accordingly, Trading account gains (losses)—net include gains and losses from transactions undertaken for trading purposes, including both market making for customers and proprietary trading, or transactions through which the Group seeks to capture gains arising from short-term changes in market value. Trading account gains (losses)—net also include gains and losses related to changes in the fair value of derivatives and other financial instruments not eligible for hedge accounting under U.S. GAAP that are utilized to offset mainly interest rate risk related to the Group’s various assets and liabilities, as well as gains and losses related to changes in the fair value of foreign currency-denominated available-for-sale securities for which the fair value option is elected in accordance with ASC 825, “Financial Instruments” (“ASC 825”). Net trading gains (losses) for the fiscal years ended March 31, 2012, 2013 and 2014 are comprised of the following:
			2012			2013			2014
			(in millions of yen)
	Trading account gains (losses)—net:
	Trading securities			227,056			468,029			80,606
	Derivative contracts:
	Interest rate contracts (1)			261,568			219,385			(79,562	)
	Foreign exchange contracts			(146,258	)		(91,300	)		(13,167	)
	Equity-related contracts (1)			(7,150	)		(59,462	)		(41,607	)
	Credit-related contracts (2)			(2,184	)		(174	)		899
	Other contracts			283			(2,378	)		(6,856	)
	Total			333,315			534,100			(59,687	)
	Foreign exchange gains (losses)—net (3)			98,054			20,514			25,631
	Net trading gains (losses)			431,369			554,614			(34,056	)
	Notes:
	-1	The net gain (loss) excluded from the assessment of the effectiveness of fair value hedges is included in the above table.
	-2	Amounts do not include the net loss of ¥3,391 million, ¥6,703 million and ¥8,660 million on the credit derivatives hedging the credit risk of loans during the fiscal years ended March 31, 2012, 2013 and 2014, respectively. The net loss is recorded in Other noninterest expenses.
	-3	Amounts include realized and unrealized gains and losses on both derivative instruments and nonderivative instruments, such as translation gains and losses related to foreign currency-denominated available-for-sale securities for which the fair value option is elected in accordance with ASC 825.

Fair_value

Fair value	12 Months Ended
	Mar. 31, 2014
Fair value	'
	28. Fair value
	Fair value measurements
	ASC 820 defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. ASC 820 also establishes a fair value hierarchy which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. In addition, ASC 820 precludes (1) the deferral of gains and losses at inception of certain derivative contracts whose fair value was not evidenced by market-observable data, and (2) the use of block discounts when measuring the fair value of instruments traded in an active market, which were previously applied to large holdings of publicly traded financial instruments.
	Fair value hierarchy
	ASC 820 specifies a hierarchy of valuation techniques based on whether the inputs to those valuation techniques are observable or unobservable. The standard describes three levels of inputs that may be used to measure fair value:
	Level 1		Quoted prices in active markets for identical assets or liabilities. Level 1 assets and liabilities include debt and equity securities and derivative contracts that are traded in an active exchange market.
	Level 2		Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 2 assets and liabilities include debt securities with quoted prices that are traded less frequently than exchange-traded instruments. If no quoted market prices are available, the fair values of debt securities and over-the-counter derivative contracts in this category are determined using a pricing model with inputs that are observable in the market or can be derived principally from or corroborated by observable market data.
	Level 3		Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Level 3 assets and liabilities include financial instruments whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation.
	Valuation process
	The MHFG Group has established clear valuation policies which govern the principles of fair value measurements and the authority and duty of each department. The Group has also established well-documented procedure manuals which describe valuation techniques and related inputs for determining the fair values of various financial instruments. The policies require that the measurement of fair values be carried out in accordance with the procedures by the risk management departments or the back offices which are independent from the front offices. The policies also require the risk management departments to check and verify whether the valuation methodologies defined in the procedure manuals are fair and proper and the internal audit departments to periodically review the compliance with the procedures throughout the Group. Although the valuation methodologies and related inputs are consistently used from period to period, a change in the market environment sometimes leads to a change in the valuation methodologies and the inputs. For instance, a change in market liquidity due to a delisting or a new listing is one of the key drivers of revisions to the valuation methodologies and the inputs. The key drivers also include the availability or the lack of market observable inputs and the development of new valuation methodologies. The price verification through the Group’s internal valuation process has an important role in identifying whether the valuation methodologies and the inputs need to be changed. The internal valuation process over the prices broker-dealers provide, primarily for Japanese securitization products, is described in more detail below in “Investments”. A change in the valuation methodologies and/or the inputs requires the revision of the valuation policies and procedure manuals, which is required to be approved by the appropriate authority, either the CEO, the head of risk management, and/or accounting, depending on the nature and characteristics of the change.
	The following is a description of valuation methodologies and inputs used for assets and liabilities measured at fair value on a recurring basis, including the general classification of such instruments pursuant to the fair value hierarchy and the MHFG Group’s valuation techniques used to measure fair values. During the fiscal year ended March 31, 2014, there were no significant changes made to the Group’s valuation techniques and related inputs.
	Trading securities and trading securities sold, not yet purchased
	When quoted prices for identical securities are available in an active market, the Group uses the quoted prices to measure the fair values of securities and such securities are classified in Level 1 of the fair value hierarchy. Level 1 securities include highly liquid government bonds and Ginnie Mae securities. When quoted prices for identical securities are available, but not actively traded, such securities are classified in Level 2 of the fair value hierarchy. When no quoted market prices are available, the Group estimates fair values by using a pricing model with inputs that are observable in the market and such securities are classified in Level 2 of the fair value hierarchy. Level 2 securities include Japanese local government bonds, corporate bonds, and commercial paper. When less liquid market conditions exist for securities, the quoted prices are stale or the prices from independent sources vary significantly, such securities are generally classified in Level 3 of the fair value hierarchy. The fair values of foreign currency denominated securitization products such as RMBS, CMBS, and ABS are determined primarily by using a discounted cash flow model. The key inputs used for the model include default rates, recovery rates, prepayment rates, and discount rates. In the event that certain key inputs are unobservable or cannot be corroborated by observable market data, these financial instruments are classified in Level 3.
	The investment funds are classified in either Level 1, Level 2, or Level 3 of the fair value hierarchy. Exchange-Traded Funds (“ETF”) are generally classified in Level 1, while the others are classified in Level 2 or Level 3. Investment trusts and hedge funds are generally classified in Level 2, since those funds are measured at the net asset value (“NAV”) per share and the Group has the ability to redeem its investment with the investees at the NAV per share at the measurement date or within the near term. In contrast, private equity funds and real estate funds measured at the NAV per share are generally classified in Level 3, since the Group does not have the ability to redeem its investment with the investees at the NAV per share, and it cannot redeem its investment with the investees at the NAV per share at the measurement date or within the near term.
	Derivative financial instruments
	Exchange-traded derivatives are valued using quoted market prices and consequently are classified in Level 1 of the fair value hierarchy. However, the majority of derivatives entered into by the Group are executed over-the-counter and are valued using internal valuation techniques as no quoted market prices are available for such instruments. The valuation techniques depend on the type of derivatives. The principal techniques used to value these instruments are discounted cash flow models and the Black-Scholes option pricing model, which are widely accepted in the financial services industry. The key inputs vary with the type of derivatives and the nature of the underlying instruments and include interest rate yield curves, foreign exchange rates, the spot price of the underlying, volatility and correlation. Each item is classified in either Level 2 or Level 3 depending on the observability of the significant inputs to the model. Level 2 derivatives include plain vanilla interest rate and currency swaps and option contracts. Derivative contracts valued using significant unobservable correlation or volatility are classified in Level 3 of the fair value hierarchy.
	Investments
	The fair values of available-for-sale securities are determined primarily using the same procedures described for trading securities above. Since private placement bonds have no quoted market prices, the fair values of such bonds are estimated based on a discounted cash flow model using interest rates approximating the current rates for instruments with similar maturities and credit risk. Private placement bonds are classified in either Level 2 or Level 3 depending on the observability of the significant inputs to the model, such as credit risk. The fair values of Japanese securitization products such as RMBS, CMBS, CDO, ABS, and CLO are generally based upon single non-binding quoted prices from broker-dealers. Such quotes are validated through the Group’s internal processes and controls. In the rare case where the Group finds the quoted prices to be invalid through its internal valuation process, it adjusts those prices or alternatively estimates their fair values by using a discounted cash flow model to incorporate the Group’s estimates of key inputs such as the most recent value of each underlying asset, cash flows of the underlying assets, and discount margin. The validation of such prices varies depending on the nature and type of the products. For the majority of RMBS, CDO, ABS and CLO products, broker quotes are validated by investigating significant unusual monthly valuation fluctuations and comparing to prices internally computed through discounted cash flow models using assumptions and parameters provided by brokers such as the cash flows of underlying assets, yield curve, prepayment speed and credit spread. For the majority of CMBS, the Group validates broker quotes through a review process that includes the investigation of significant unusual monthly valuation fluctuations and/or a review of underlying assets with significant differences between the valuations of the Group and the broker-dealers being identified. Though most Japanese securitization products are classified in Level 3, certain securitization products such as Japanese RMBS are classified in Level 2, if the quoted prices are verified through either recent market transactions or a pricing model that can be corroborated by observable market data.
	Other investments, except investments held by consolidated investment companies, have not been measured at fair value on a recurring basis. Investments held by consolidated investment companies mainly consist of marketable and non-marketable equity securities and debt securities. The fair value of the marketable equity securities is based upon quoted market prices. The fair value of the non-marketable equity securities is based upon significant management judgment, as very limited quoted prices exist. When evaluating such securities, the Group firstly considers recent market transactions of identical securities, if applicable. Subsequently, the Group uses commonly accepted valuation techniques such as earnings multiples based on comparable public securities. Non-marketable equity securities are generally classified in Level 3 of the fair value hierarchy. The fair value of the debt securities is estimated using a discounted cash flow model, since they have no quoted market prices. Those debt securities are classified in Level 3, because the credit risk is unobservable.
	Long-term debt
	Where fair value accounting has been elected for structured notes, the fair values are determined by incorporating the fair values of embedded derivatives that are primarily derived by using the same procedures described for derivative financial instruments above. Such instruments are classified in Level 2 or Level 3 depending on the observability of significant inputs to the model of the embedded derivatives.
	Items measured at fair value on a recurring basis
	Assets and liabilities measured at fair value on a recurring basis at March 31, 2013 and 2014, including those for which the MHFG Group has elected the fair value option, are summarized below:
	2013		Level 1			Level 2			Level 3			Assets/
												Liabilities
												measured
												at fair value
			(in billions of yen)
	Assets:
	Trading securities (1):
	Japanese government bonds			4,651			49			—			4,700
	Japanese local government bonds			—			125			—			125
	U.S. Treasury bonds and federal agency securities			5,777			306			—			6,083
	Other foreign government bonds			2,235			194			—			2,429
	Agency mortgage-backed securities			2,055			596			—			2,651
	Residential mortgage-backed securities			—			—			100			100
	Commercial mortgage-backed securities			—			3			91			94
	Certificates of deposit and commercial paper			—			1,318			—			1,318
	Corporate bonds and other			50			1,176			417			1,643
	Equity securities			622			503			71			1,196
	Derivatives:
	Interest rate contracts			7			10,319			24			10,350
	Foreign exchange contracts			5			3,066			28			3,099
	Equity-related contracts			45			114			23			182
	Credit-related contracts			—			30			29			59
	Other contracts			—			18			20			38
	Available-for-sale securities:
	Japanese government bonds			29,198			1,585			—			30,783
	Japanese local government bonds			—			244			—			244
	U.S. Treasury bonds and federal agency securities			178			—			—			178
	Other foreign government bonds			334			264			—			598
	Agency mortgage-backed securities			144			862			—			1,006
	Residential mortgage-backed securities			—			150			292			442
	Commercial mortgage-backed securities			—			—			250			250
	Japanese corporate bonds and other debt securities			—			2,000			215			2,215
	Foreign corporate bonds and other debt securities			12			345			202			559
	Equity securities (marketable)			2,975			164			—			3,139
	Other investments			1			—			75			76
	Total assets measured at fair value on a recurring basis (2)			48,289			23,431			1,837			73,557
	Liabilities:
	Trading securities sold, not yet purchased			3,338			182			—			3,520
	Derivatives:
	Interest rate contracts			8			9,997			13			10,018
Foreign exchange contracts			4			2,968			11			2,983
Equity-related contracts			51			110			16			177
Credit-related contracts			—			35			9			44
Other contracts			—			8			19			27
Long-term debt (3)			—			171			381			552
Total liabilities measured at fair value on a recurring basis			3,401			13,471			449			17,321
2014		Level 1			Level 2			Level 3			Assets/
											Liabilities
											measured
											at fair value
		(in billions of yen)
Assets:
Trading securities (1):
Japanese government bonds			3,360			50			—			3,410
Japanese local government bonds			—			74			—			74
U.S. Treasury bonds and federal agency securities			3,541			486			—			4,027
Other foreign government bonds			2,567			274			—			2,841
Agency mortgage-backed securities			1,390			364			—			1,754
Residential mortgage-backed securities			—			—			78			78
Commercial mortgage-backed securities			—			2			91			93
Certificates of deposit and commercial paper			—			969			—			969
Corporate bonds and other			38			1,671			413			2,122
Equity securities			714			579			60			1,353
Derivatives:
Interest rate contracts			43			7,997			24			8,064
Foreign exchange contracts			6			2,331			17			2,354
Equity-related contracts			60			124			13			197
Credit-related contracts			—			28			21			49
Other contracts			1			18			4			23
Available-for-sale securities:
Japanese government bonds			20,912			1,144			—			22,056
Japanese local government bonds			—			245			—			245
U.S. Treasury bonds and federal agency securities			154			—			—			154
Other foreign government bonds			280			441			—			721
Agency mortgage-backed securities			105			856			—			961
Residential mortgage-backed securities			—			112			220			332
Commercial mortgage-backed securities			—			—			161			161
Japanese corporate bonds and other debt securities			—			1,858			170			2,028
Foreign corporate bonds and other debt securities			1			427			141			569
Equity securities (marketable)			3,348			74			—			3,422
Other investments			2			—			69			71
Total assets measured at fair value on a recurring basis (2)			36,522			20,124			1,482			58,128
Liabilities:
Trading securities sold, not yet purchased			3,862			488			—			4,350
Derivatives:
Interest rate contracts			42			7,846			7			7,895
Foreign exchange contracts			5			2,340			6			2,351
Equity-related contracts			58			108			12			178
Credit-related contracts			—			30			4			34
Other contracts			1			12			4			17
Long-term debt (3)			—			157			501			658
Total liabilities measured at fair value on a recurring basis			3,968			10,981			534			15,483
Notes:
-1	Trading securities include foreign currency denominated securities for which the MHFG Group elected the fair value option.
-2	Amounts include the investments measured at the NAV per share at March 31, 2013 and 2014, of ¥715 billion and ¥649 billion, respectively, of which ¥667 billion and ¥612 billion, respectively, are classified in Level 2, and ¥48 billion and ¥37 billion, respectively, are classified in Level 3. The amounts of unfunded commitments related to these investments at March 31, 2013 and 2014 were ¥24 billion and ¥23 billion, respectively.
-3	Amounts represent items for which the Group elected the fair value option.
Items measured at fair value on a recurring basis using significant unobservable inputs (Level 3)
The following table presents a reconciliation for all assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the fiscal years ended March 31, 2013 and 2014:
2013		April 1,			Gains			Gains			Transfers			Transfers			Purchases			Sales			Issuances		Settlements			March 31,		Change in
		2012			(losses) in			(losses)			into			out of														2013		unrealized
					Earnings			in OCI			Level 3			Level 3																gains
																														(losses)
																														still held (6)
		(in billions of yen)
Assets:
Trading securities:
Residential mortgage-			159			17	(2)		—			—			—			2			(7	)		—		(71	)		100		6
backed securities
Commercial mortgage-			26			1	(2)		—			—			—			72			(1	)		—		(7	)		91		—
backed securities
Corporate bonds and other			355			72	(2)		—			14			(8	)		609			(544	)		—		(81	)		417		42
Equity securities			82			4	(2)		—			3			(3	)		10			(25	)		—		—			71		(1	)
Derivatives, net (1):
Interest rate contracts			(10	)		16	(2)		—			—			—			—			—			—		5			11		16
Foreign exchange contracts			37			(18	)(2)		—			—			(8	)		—			—			—		6			17		(21	)
Equity-related contracts			22			(10	)(2)		—			—			—			—			—			—		(5	)		7		(10	)
Credit-related contracts			23			(6	)(2)		—			(1	)		1			—			—			—		3			20		(5	)
Other contracts			15			—	(2)		—			—			(14	)		—			—			—		—			1		—
Available-for-sale securities:
Residential mortgage-			348			—	(3)		6	(4)		—			—			29			(1	)		—		(90	)		292		—
backed securities
Commercial mortgage-			330			2	(3)		12	(4)		—			—			31			(16	)		—		(109	)		250		(5	)
backed securities
Japanese corporate			226			—	(3)		1	(4)		—			—			95			—			—		(107	)		215		—
bonds and other debt securities
Foreign corporate bonds			236			4	(3)		6	(4)		—			—			28			(4	)		—		(68	)		202		—
and other debt securities
Other investments			189			12	(3)		—			—			—			6			(49	)		—		(83	)		75		—
Liabilities:
Trading securities sold, not yet purchased			—			—	(2)		—			—			(1	)		(41	)		42			—		—			—		—
Long-term debt			460			(26	)(5)		—			4			(175	)		—			—			142		(76	)		381		(24	)
2014		April 1,			Gains			Gains			Transfers			Transfers			Purchases			Sales			Issuances		Settlements			March 31,		Change in
		2013			(losses) in			(losses)			into			out of														2014		unrealized
					Earnings			in OCI			Level 3			Level 3																gains
																														(losses)
																														still held (6)
		(in billions of yen)
Assets:
Trading securities:
Residential mortgage-backed securities			100			10	(2)		—			—			—			—			(4	)		—		(28	)		78		7
Commercial mortgage-backed securities			91			5	(2)		—			—			—			—			—			—		(5	)		91		4
Corporate bonds and other			417			55	(2)		—			4			(12	)		503			(442	)		—		(112	)		413		35
Equity securities			71			6	(2)		—			—			—			8			(24	)		—		(1	)		60		—
Derivatives, net (1):
Interest rate contracts			11			6	(2)		—			(1	)		—			—			—			—		1			17		11
Foreign exchange contracts			17			(3	)(2)		—			—			—			—			—			—		(3	)		11		5
Equity-related contracts			7			(6	)(2)		—			—			—			—			—			—		—			1		(7	)
Credit-related			20			(6	)(2)		—			—			1			—			—			—		2			17		(6	)
contracts
Other contracts			1			—	(2)		—			—			—			—			—			—		(1	)		—		—
Available-for-sale securities:
Residential mortgage-backed securities			292			(1	)(3)		5	(4)		—			—			5			(9	)		—		(72	)		220		—
Commercial mortgage-backed securities			250			5	(3)		(2	)(4)		—			—			36			(18	)		—		(110	)		161		(1	)
Japanese corporate			215			—	(3)		—	(4)		—			(30	)		60			(1	)		—		(74	)		170		—
bonds and other debt securities
Foreign corporate bonds and other debt securities			202			8	(3)		(1	)(4)		7			—			—			—			—		(75	)		141		—
Other investments			75			(2	)(3)		—			—			(2	)		7			(2	)		—		(7	)		69		(2	)
Liabilities:
Long-term debt			381			4	(5)		—			1			(1	)		—			—			197		(73	)		501		5
Notes:
-1	Total Level 3 derivative exposures have been netted on the table for presentation purposes only.
-2	Gains (losses) in Earnings are reported in Trading account gains (losses)—net, Foreign exchange gains (losses)—net or Other noninterest income (expenses).
-3	Gains (losses) in Earnings are reported in Investment gains (losses)—net.
-4	Gains (losses) in OCI are reported in Accumulated other comprehensive income (loss).
-5	Gains (losses) in Earnings are reported in Other noninterest income (expenses).
-6	Amounts represent total gains or losses recognized in earnings during the period. These gains or losses are attributable to the change in fair value relating to assets and liabilities classified as Level 3 that are still held at March 31, 2013 and 2014.
Transfers between levels
Transfers of assets or liabilities between levels of the fair value hierarchy are assumed to occur at the beginning of the period.
During the fiscal year ended March 31, 2013, ¥37 billion of Trading securities were transferred from Level 1 to Level 2. Transfers of Trading securities were primarily due to certain Japanese government bonds and foreign corporate bonds which were traded with less frequency.
During the fiscal year ended March 31, 2013, ¥17 billion of Trading securities and ¥1 billion of net Derivative liabilities were transferred into Level 3. Transfers of Trading securities were primarily due to decreased liquidity for certain foreign corporate bonds and equity securities. Transfers of net Derivative liabilities were primarily due to decreased price observability for certain credit derivatives. During the fiscal year ended March 31, 2013, ¥11 billion of Trading securities, ¥1 billion of Trading securities sold, not yet purchased and ¥21 billion of net Derivative assets were transferred out of Level 3. Transfers of Trading securities and Trading securities sold, not yet purchased were primarily due to increased liquidity for certain Japanese and foreign corporate bonds and equity securities. Transfers of net Derivative assets were primarily due to increased price observability for certain commodity derivatives and foreign exchange derivatives. During the fiscal year ended March 31, 2013, ¥4 billion of transfers into Level 3 and ¥175 billion of transfers out of Level 3 for Long-term debt were primarily due to changes in the impact of unobservable inputs on the value of certain structured notes.
During the fiscal year ended March 31, 2014, the transfers into Level 3 included ¥4 billion of Trading securities, ¥1 billion of net Derivative liabilities, ¥7 billion of Available-for-sale securities and ¥1 billion of Long-term debt. Transfers into Level 3 for Trading securities and Available-for-sale securities were primarily due to decreased liquidity for certain foreign corporate bonds. Transfers into Level 3 for net Derivative liabilities were primarily due to decreased price observability for certain interest rate derivatives. Transfers into Level 3 for Long-term debt were primarily due to changes in the impact of unobservable inputs on the value of certain structured notes. During the fiscal year ended March 31, 2014, the transfers out of Level 3 included ¥12 billion of Trading securities, ¥1 billion of net Derivative liabilities, ¥30 billion of Available-for-sale securities, ¥2 billion of Other investments and ¥1 billion of Long-term debt. Transfers out of Level 3 for Trading securities were primarily due to increased liquidity for certain foreign corporate bonds. Transfers out of Level 3 for net Derivative liabilities were primarily due to increased price observability for certain credit derivatives. Transfers out of Level 3 for Available-for-sale securities were primarily due to increased liquidity for certain Japanese corporate bonds and other debt securities. Transfers out of Level 3 for Other investments were caused by a new listing of certain non-marketable equity securities. Transfers out of Level 3 for Long-term debt were primarily due to changes in the impact of unobservable inputs on the value of certain structured loans.
Quantitative information about Level 3 fair value measurements
The following table presents information about significant unobservable inputs related to the MHFG Group’s material classes of Level 3 assets and liabilities at March 31, 2013 and 2014:
2013
Products/Instruments		Fair value			Principal valuation technique		Unobservable inputs	Range of input values
(in billions of yen, except for ratios and basis points)
Trading securities and Available-for-sale securities:
Residential mortgage-backed securities			392		Discounted cash flow		Prepayment rate		0%–24%
					Price-based		Default rate		0%–5%
							Recovery rate		70%–100%
							Discount margin		7bps–2,616bps
Commercial mortgage-backed securities			341		Discounted cash flow		Discount margin		9bps–3,929bps
					Price-based
Corporate bonds and other debt securities			834		Discounted cash flow		Prepayment rate (1)		0%–43%
					Price-based		Default rate (1)		0%–8%
							Recovery rate (1)		15%–85%
							Discount margin (1)		0bps–4,918bps
							Discount margin (2)		0bps–1,232bps
Derivatives, net:
Interest rate contracts			11		Internal valuation model (3)		IR – IR correlation		42%–100%
							Default rate (4)		0%–63%
Foreign exchange contracts			17		Internal valuation model (3)		FX – IR correlation		36%–55%
							FX – FX correlation		55%–55%
							FX volatility		16%–26%
							Default rate (4)		0%–63%
Equity-related contracts			7		Internal valuation model(3)		Equity – IR correlation		0%–60%
							Equity – FX correlation		0%–70%
							Equity volatility		14%–48%
Credit-related contracts (5)			20		Internal valuation model (3)		Default rate		0%–67%
							Credit correlation		2%–100%
Long-term debt			381		Internal valuation model (3)		IR – IR correlation		42%–100%
							FX – IR correlation		36%–55%
							FX – FX correlation		55%–55%
							Equity – IR correlation		0%–60%
							Equity volatility		18%–48%
							Default rate		0%–10%
							Credit correlation		2%–100%
2014
Products/Instruments		Fair value			Principal valuation technique		Unobservable inputs	Range of input values
(in billions of yen, except for ratios and basis points)
Trading securities and Available-for-sale securities:
Residential mortgage-backed securities			298		Discounted cash flow		Prepayment rate		1%–24%
					Price-based		Default rate		0%–4%
							Recovery rate		70%–100%
							Discount margin		8bps–2,002bps
Commercial mortgage-backed securities			252		Discounted cash flow		Discount margin		17bps – 3,441bps
					Price-based
Corporate bonds and other debt securities			724		Discounted cash flow		Prepayment rate (1)		0%–42%
					Price-based		Default rate (1)		0%–9%
							Recovery rate (1)		15%–75%
							Discount margin (1)		12bps–1,725bps
							Discount margin (2)		-122bps–1,303bps
Derivatives, net:
Interest rate contracts			17		Internal valuation model (3)		IR – IR correlation		23%–100%
							Default rate (4)		0%–63%
Foreign exchange contracts			11		Internal valuation model (3)		FX – IR correlation		28%–52%
							FX – FX correlation		55%–55%
							FX volatility		14%–25%
							Default rate (4)		0%–63%
Equity-related contracts			1		Internal valuation model (3)		Equity – IR correlation		0%–60%
							Equity – FX correlation		0%–70%
							Equity volatility		18%–35%
Credit-related contracts (5)			17		Internal valuation model (3)		Default rate		0%–47%
							Credit correlation		1%–100%
Long-term debt			501		Internal valuation model (3)		IR – IR correlation		23%–100%
							FX – IR correlation		28%–52%
							FX – FX correlation		55%–55%
							Equity – IR correlation		0%–60%
							Equity – FX correlation		0%–70%
							Equity volatility		13%–37%
							Default rate		0%–5%
							Credit correlation		19%–100%
Notes:
-1	These inputs are mainly used for determining the fair values of securitization products such as CDO, CLO and ABS, other than RMBS and CMBS.
-2	This input is mainly used for determining the fair values of Japanese corporate bonds and foreign corporate bonds.
-3	Internal valuation model includes discounted cash flow models and the Black-Scholes option pricing model.
-4	This input represents the counterparty default rate derived from the MHFG Group’s own internal credit analysis.
-5	The majority of the fair value of credit derivatives in Level 3 relates to credit derivatives economically hedging the credit risk in certain securitization products. The unobservable inputs of these credit derivatives have already been included in the unobservable inputs related to Trading securities and Available-for-sale securities disclosed above.
IR =nterest rate
FX =oreign exchange
Sensitivity to unobservable inputs and interrelationship between unobservable inputs
The following is a description of the sensitivities and interrelationships of the significant unobservable inputs used to measure the fair values of Level 3 assets and liabilities.
(1) Prepayment rate
The prepayment rate is the estimated rate at which voluntary unscheduled repayments of the principal of the underlying assets are expected to occur. The movement of the prepayment rate is generally negatively correlated with borrower delinquency. A change in prepayment rate would impact the valuation of the fair values of financial instruments either positively or negatively, depending on the structure of financial instruments.
(2) Default rate
The default rate is an estimate of the likelihood of not collecting contractual payments. An increase in the default rate would generally be accompanied by a decrease in the recovery rate and an increase in the discount margin. It would also generally impact the valuation of the fair values of financial instruments negatively.
(3) Recovery rate
The recovery rate is an estimate of the percentage of contractual payments that would be collected in the event of a default. An increase in recovery rate would generally be accompanied by a decrease in the default rate. It would also generally impact the valuation of the fair values of financial instruments positively.
(4) Discount margin
The discount margin is the portion of the interest rate over a benchmark market interest rate such as LIBOR or swap rates. It primarily consists of a risk premium component which is the amount of compensation that market participants require due to the uncertainty inherent in the financial instruments’ cash flows resulting from credit risk. An increase in discount margin would generally impact the valuation of the fair values of financial instruments negatively.
(5) Correlation
Correlation is the likelihood of the movement of one input relative to another based on an established relationship. The change in correlation would impact the valuation of derivatives either positively or negatively, depending on the nature of the underlying assets.
(6) Volatility
Volatility is a measure of the expected change in variables over a fixed period of time. Some financial instruments benefit from an increase in volatility and others benefit from a decrease in volatility. Generally, for a long position in an option, an increase in volatility would result in an increase in the fair values of financial instruments.
Items measured at fair value on a nonrecurring basis
Certain assets and liabilities are measured at fair value on a nonrecurring basis and are not included in the tables above. These assets and liabilities primarily include items that are measured at the lower of cost or fair value, and items that were initially measured at cost and have been written down to fair value as a result of impairment. The following table shows the fair value hierarchy for these items as of March 31, 2013 and 2014.
2013		Total			Level 1			Level 2			Level 3			Aggregate cost
		(in billions of yen)
Assets:
Loans			222			—			—			222			343
Loans held-for-sale			5			—			5			—			5
Other investments			11			—			—			11			16
Premises and equipment—net			1			—			—			1			5
Total assets at fair value on a nonrecurring basis			239			—			5			234			369
2014		Total			Level 1			Level 2			Level 3			Aggregate cost
		(in billions of yen)
Assets:
Loans			124			—			—			124			208
Loans held-for-sale			33			—			—			33			34
Other investments			5			—			—			5			6
Premises and equipment—net			1			—			—			1			2
Goodwill			—			—			—			—			4
Total assets at fair value on a nonrecurring basis			163			—			—			163			254
Loans in the table above have been impaired and measured based upon the fair value of the underlying collateral.
Loans held-for-sale in the table above are accounted for at the lower of cost or fair value at the end of the period. The items for which fair values are determined by using actual or contractually determined selling price data are classified as Level 2. Due to the lack of current observable market information, the determination of the fair values for items other than the aforementioned requires significant adjustment based upon management judgment and estimation, which results in such items being classified in Level 3 of the hierarchy.
Other investments in the table above, which consist of certain equity method investments and non-marketable equity securities, have been impaired and written down to fair value. The fair values of the impaired marketable equity method investments are determined by their quoted market prices. As the securities are traded on an active exchange market, they are classified as Level 1. The fair values of the impaired non-marketable equity securities, which include non-marketable equity method investments, are determined primarily by using a liquidation value technique. As significant management judgment or estimation is required in the determination of the fair values of non-marketable equity securities, they are classified as Level 3.
Premises and equipment—net in the table above have been impaired and written down to fair value.
Goodwill in the table above is entirely related to PT. Mizuho Balimor Finance reporting unit. Due to the decline of the fair value of the reporting unit, the carrying amount of the goodwill was reduced to its fair value and an impairment loss was recognized. As the determination of fair value of the goodwill required significant management judgment and estimation, the item is classified as Level 3.
Fair value option
The MHFG Group elected the fair value option for certain eligible financial instruments described below.
Foreign currency denominated available-for-sale securities
Prior to the adoption of the fair value option in accordance with ASC 825, the changes in fair value of foreign currency denominated available-for-sale securities had been accounted for in AOCI, while the changes in fair value caused by foreign exchange fluctuation of foreign currency denominated financial liabilities had been accounted for in earnings. The MHFG Group elected the fair value option for those securities to mitigate the volatility in earnings due to the difference in the recognition of foreign exchange risk between available-for-sale securities and financial liabilities. Following the election of the fair value option, these securities have been reported as trading securities in Trading account assets.
Certain hybrid financial instruments
The MHFG Group issues structured notes as part of its client-driven activities. Structured notes are debt instruments that contain embedded derivatives. The Group elected the fair value option for certain structured notes to mitigate accounting mismatches and to achieve operational simplifications. Following the election of the fair value option, these structured notes continue to be reported in Long-term debt and interest on these structured notes continues to be reported in Interest expense on long-term debt based on the contractual rates. The differences between the aggregate fair value of these structured notes for which the fair value option has been elected and the aggregate unpaid principal balance of such instruments were ¥9 billion and ¥14 billion at March 31, 2013 and 2014, respectively. The net unrealized gains (losses) resulting from changes in fair values of these structured notes of ¥(30) billion and ¥4 billion, which included the fair value changes attributable to changes in the Group’s own credit risk, were recorded in Other noninterest income (expenses) for the fiscal years ended March 31, 2013 and 2014, respectively.
Fair value of financial instruments
ASC 825 requires the disclosure of the estimated fair value of financial instruments. The fair value of financial instruments is the amount that would be exchanged between willing parties, other than in a forced sale or liquidation. Quoted market prices, if available, are best utilized as estimates of the fair values of financial instruments. However, since no quoted market prices are available for certain financial instruments, fair values for such financial instruments have been estimated based on management’s assumptions, discounted cash flow models or other valuation techniques. Such estimation methods are described in more detail below. These estimates could be significantly affected by different sets of assumptions. There are certain limitations to management’s best judgment in estimating fair values of financial instruments and inherent subjectivity involved in estimation methodologies and assumptions used to estimate fair value. Accordingly, the net realizable or liquidation values could be materially different from the estimates presented below.
ASC 825 does not require the disclosure of the fair value of nonfinancial instruments.
The following is a description of the valuation methodologies used for estimating the fair value for financial assets and liabilities not carried at fair value on the MHFG Group’s consolidated balance sheets.
Cash and due from banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions
The carrying value of short-term financial assets, such as cash and due from banks, interest-bearing deposits in other banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions approximates the fair value of these assets since they generally involve limited losses from credit risk or have short-term maturities with interest rates that approximate market rates.
Investments
The fair value of held-to-maturity securities is determined primarily by using the same procedures, and techniques described for trading securities and available-for-sale securities aforementioned in this section. The fair value of other equity interests, which primarily comprise non-marketable equity securities, is not readily determinable, and their carrying amounts of ¥537 billion and ¥526 billion at March 31, 2013 and 2014, respectively, were not included in the disclosure.
Loans
Performing loans have been fair valued as groups of similar loans based on the type of loan, credit quality, prepayment assumptions and remaining maturity. The fair value of performing loans is determined based on discounted cash flows using interest rates approximating the MHFG Group’s current rates for similar loans. The fair value of impaired loans is determined based on either discounted cash flows incorporating the Group’s best estimate of the expected future cash flows or the fair value of the underlying collateral, if impaired loans are collateral dependent.
Other financial assets
The carrying value of other financial assets, which primarily consist of accounts receivable from brokers, dealers, and customers for securities transactions, accrued income and collateral provided for derivative transactions, approximates the fair value of these assets since they generally involve limited losses from credit risk or have short-term maturities with interest rates that approximate market rates. The majority of other financial assets is classified as Level 2, and included in the table of Note 12 “Other assets and liabilities”.
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions
The carrying value of short-term financial liabilities, such as noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions approximates the fair value of these liabilities since they generally have short-term maturities with interest rates that approximate market rates.
Interest-bearing deposits
The carrying value of demand deposits approximates the fair value since it represents the amount payable on demand at the balance sheet date. The fair value of time deposits and certificates of deposit is primarily estimated based on discounted cash flow analysis using current interest rates for instruments with similar maturities. The carrying value of short-term certificates of deposit approximates the fair value.
Due to trust accounts
The carrying value of due to trust accounts approximates the fair value since they generally have short-term maturities with interest rates that approximate market rates.
Other short-term borrowings
The carrying value of the majority of short-term borrowings approximates the fair value since they generally have short-term maturities with interest rates that approximate market rates. The fair value of certain borrowings is estimated based on discounted cash flow analysis using interest rates approximating the MHFG Group’s incremental borrowing rates for instruments with similar maturities.
Long-term debt
Long-term debt is fair valued using quoted market prices, if available. Otherwise, the fair value of long-term debt is estimated based on discounted cash flow analysis using interest rates approximating the MHFG Group’s incremental borrowing rates for instruments with similar maturities.
Other financial liabilities
The carrying value of other financial liabilities, which primarily consist of accounts payable to brokers, dealers, and customers for securities transactions, accrued expenses and collateral accepted for derivative transactions, approximates the fair value since they generally have short-term maturities with interest rates that approximate market rates. The majority of other financial liabilities is classified as Level 2, and included in the table of Note 12 “Other assets and liabilities”.
The fair value of certain off-balance-sheet financial instruments, such as commitments to extend credit and commercial letters of credit, is not considered material to the consolidated balance sheets at March 31, 2013 and 2014.
The following table shows the carrying amounts and fair values at March 31, 2013 and 2014, of certain financial instruments, excluding financial instruments which are carried at fair value on a recurring basis and those outside the scope of ASC 825 such as the equity method investments and lease contracts as defined in ASC 840, “Leases” (“ASC 840”) :
		2013
		Carrying			Estimated fair value
		amount			Total			Level 1			Level 2			Level 3
		(in billions of yen)
Financial assets:
Cash and due from banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions			27,583			27,583			903			26,680			—
Investments			3,000			3,020			3,020			—			—
Loans, net of allowance for loan losses (Note)			69,028			70,261			—			—			70,261
Financial liabilities:
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions			48,048			48,048			12,796			35,252			—
Interest-bearing deposits			87,247			87,210			34,596			52,614			—
Due to trust accounts			619			619			—			619			—
Other short-term borrowings			6,724			6,723			—			6,723			—
Long-term debt			8,235			8,598			—			7,967			631
		2014
		Carrying			Estimated fair value
		amount			Total			Level 1			Level 2			Level 3
		(in billions of yen)
Financial assets:
Cash and due from banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions			34,563			34,563			1,437			33,126			—
Investments			4,040			4,058			4,058			—			—
Loans, net of allowance for loan losses (Note)			72,801			73,975			—			—			73,975
Financial liabilities:
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions			44,124			44,124			13,543			30,581			—
Interest-bearing deposits			88,744			88,705			37,394			51,311			—
Due to trust accounts			742			742			—			742			—
Other short-term borrowings			6,024			6,024			—			6,024			—
Long-term debt			9,176			9,441			—			8,600			841
Note: Loans, net of allowance for loan losses include items measured at fair value on a nonrecurring basis.

Offsetting_of_financial_assets

Offsetting of financial assets and financial liabilities	12 Months Ended
	Mar. 31, 2014
Offsetting of financial assets and financial liabilities	'
	29. Offsetting of financial assets and financial liabilities
	Derivatives
	The MHFG Group enters into master netting arrangements such as International Swaps and Derivatives Association, Inc. (“ISDA”) or similar agreements with counterparties to manage mainly credit risks associated with counterparty default. If the predetermined events including counterparty default occur, these enforceable master netting arrangements or similar agreements give the Group the right to offset derivative receivables and derivative payables and related financial collateral such as cash and securities with the same counterparty.
	Repurchase and resale agreements and securities lending and borrowing transactions
	Repurchase and resale agreements and securities lending and borrowing transactions are generally covered by industry standard master repurchase agreements and industry standard master securities lending agreements with netting terms to manage mainly credit risks associated with counterparty default. In the event of default by the counterparty, these agreements with netting terms provide the Group with the right to offset receivables and payables related to such transactions with the same counterparty, and to liquidate the collateral held.
	The following tables provide information about the offsetting of financial assets and financial liabilities at March 31, 2013 and 2014. The tables include derivatives, repurchase and resale agreements, and securities lending and borrowing transactions that are subject to enforceable master netting arrangements or similar agreements irrespective of whether or not they are offset on the Group’s consolidated balance sheets.
									Amounts not offset on
									the balance sheet(3)
			Gross amounts		Gross amounts		Net amounts		Financial		Cash		Net
			recognized		offset on the		presented on the		instruments(4)		collateral		amounts
					balance sheet		balance sheet(2)
			(in billions of yen)
	2013
	Assets (1):
	Derivatives			13,019		—		13,019		11,289		446		1,284
	Receivables under resale agreements			8,869		—		8,869		8,812		—		57
	Receivables under securities borrowing transactions			5,544		—		5,544		5,534		—		10
	Total			27,432		—		27,432		25,635		446		1,351
	Liabilities (1):
	Derivatives			12,712		—		12,712		11,234		653		825
	Payables under repurchase agreements			17,397		—		17,397		17,280		—		117
	Payables under securities lending transactions			11,326		—		11,326		11,320		—		6
	Total			41,435		—		41,435		39,834		653		948
	2014
	Assets (1):
	Derivatives			9,880		—		9,880		8,702		406		772
	Receivables under resale agreements			8,236		—		8,236		8,200		—		36
	Receivables under securities borrowing transactions			4,990		—		4,990		4,978		—		12
	Total			23,106		—		23,106		21,880		406		820
	Liabilities (1):
	Derivatives			9,648		—		9,648		8,621		431		596
	Payables under repurchase agreements			16,690		—		16,690		16,667		—		23
	Payables under securities lending transactions			6,085		—		6,085		6,082		—		3
	Total			32,423		—		32,423		31,370		431		622
	Notes:
	-1	Amounts relating to master netting arrangements or similar agreements where the Group does not have the legal right of set-off or where uncertainty exists as to the enforceability of these agreements are excluded. For derivatives, the table includes amounts relating to over-the-counter (“OTC”) and OTC-cleared derivatives that are subject to enforceable master netting arrangements or similar agreements.
	-2	Derivative assets and liabilities are recorded in Trading account assets and Trading account liabilities, respectively.
	-3	Amounts do not exceed the net amounts presented on the balance sheet and do not include the effect of overcollateralization, where it exists.
	-4	For derivatives, amounts include derivative assets or liabilities and securities collateral that are eligible for offsetting under enforceable master netting arrangements or similar agreements.

Related_party_transactions

Related party transactions	12 Months Ended
	Mar. 31, 2014
Related party transactions	'
	30. Related party transactions
	Transactions with directors, executive officers, and their associates
	The banking subsidiaries of MHFG make loans to the MHFG Group’s directors, executive officers, and their associates in their ordinary course of business. At March 31, 2013 and 2014, outstanding loans to such related parties were not considered significant. These related party loans were made on substantially the same terms, including interest rate and collateral, as those prevailing at the same time for comparable transactions with unrelated parties. At March 31, 2013 and 2014, there were no loans to these related parties that were considered impaired.
	Other transactions, such as deposits, were entered into between MHFG’s subsidiaries and the MHFG Group’s directors, executive officers, and their associates during the fiscal years ended March 31, 2012, 2013 and 2014. The outstanding amounts of these transactions, which were made in the ordinary course of business with terms equivalent to those with unrelated parties, were not considered significant.
	Transactions with other related parties
	A number of transactions were entered into with other related parties, such as MHFG’s employees and affiliates accounted for under the equity method. These transactions included loans, deposits, and other banking services. They were not significant in amount and were conducted with substantially the same terms as those for comparable transactions with unrelated parties.

Business_segment_information

Business segment information	12 Months Ended
	Mar. 31, 2014
Business segment information	'
	31. Business segment information
	Under U.S. GAAP, companies report segment information based on the way management disaggregates the company for making operating decisions. The MHFG Group’s operating segments are based on the nature of the products and services provided, the type of customer and the Group’s management organization. The business segment information set forth below is derived from the internal management reporting systems used by management to measure the performance of the Group’s business segments. The management measures the performance of each of the operating segments primarily in terms of “net business profits” in accordance with internal managerial accounting rules and practices. Net business profits is used in Japan as a measure of the profitability of core banking operations, and is defined as gross profits (or the sum of net interest income, fiduciary income, net fee and commission income, net trading income and net other operating income) less general and administrative expenses. Measurement by net business profits is required for regulatory reporting to the Financial Services Agency. Therefore, the format and information are presented primarily on the basis of Japanese GAAP and are not consistent with the consolidated financial statements prepared in accordance with U.S. GAAP. A reconciliation is provided for the segments’ total net business profits with Income before income tax expense under U.S. GAAP.
	Beginning on April 1, 2013, the MHFG Group moved to a new group operational structure and established ten business units such as Personal Banking, Retail Banking, Corporate Banking (Large Corporations), etc., and head-office coordination divisions to determine strategies and initiatives across the group-wide banking, trust banking, securities, and other business areas, based on the ten business units across MHBK (the former MHBK and the former MHCB merged on July 1, 2013), MHTB, MHSC, etc. The MHFG Group realigned the reportable segments to reflect the new organizational structure.
	The MHFG Group engages in banking, trust banking, securities, and other businesses through its subsidiaries and affiliates. As these subsidiaries and affiliates are in different industries and regulatory environments, MHFG discloses business segment information based on the relevant principal consolidated subsidiaries such as MHBK (the former MHBK and the former MHCB), MHTB, and MHSC for investors to measure the present and future cash flows properly.
	Operating segments of MHBK are aggregated based on the type of customer characteristics, and are aggregated into the following seven reportable segments: Personal Banking; Retail Banking; Corporate Banking (Large Corporations); Corporate Banking; Financial Institutions & Public Sector Business; International Banking; and Trading and others.
	MHBK
	Personal Banking
	This segment provides financial products and services, such as housing loans, deposits, investment trusts, and individual insurance to individual customers through MHBK’s nationwide branches and ATM network as well as telephone and the internet banking services. In addition, this segment handles trust products as an agent of MHTB.
	Retail Banking
	This segment provides financial products and services, such as comprehensive consulting services of business succession and asset inheritance and asset management for business owners and high-net-worth customers. This segment also provides overall banking services for SMEs.
	Corporate Banking (Large Corporations)
	This segment provides a full range of financial solutions on a global basis to Japanese large corporations and their affiliates by integrating the Group’s specialty functions including banking, trust, and securities, based on solid relationships with MHBK’s domestic customers, and by utilizing its global industry knowledge.
	Corporate Banking
	This segment provides, to larger SMEs, financial products and services including a range of solution businesses in accordance with the growth strategy of MHBK’s corporate customers. This segment provides solutions for stable fund-raising, mergers and acquisitions, and initial public offerings for customers in their start-up or growth stages, and management buy-out, business succession, entry to new business, and business restructuring for customers in mature or transition stages.
	Financial Institutions & Public Sector Business
	This segment provides advisory services and solutions such as advice on financial strategy and risk management to financial institutions and provides comprehensive financial products and services that include funding support via the subscription and underwriting of bonds etc., to public sector entities.
	International Banking
	This segment provides unified support both in Japan and overseas for MHBK’s Japanese corporate customers to expand their overseas operations, and also promotes business with non-Japanese corporate customers in various countries through its global network. Further, this segment offers products such as project finance and trade finance for overseas customers.
	Trading and others
	This segment provides derivatives and other risk hedging products to satisfy MHBK’s customers’ financial and business risk control requirements. It is also engaged in MHBK’s proprietary trading, such as foreign exchange and bond trading, and asset and liability management. This segment also includes costs incurred by the head office functions of MHBK.
	MHTB
	MHTB provides products and services related to trust, real estate, securitization and structured finance, pension and asset management, and stock transfers.
	MHSC
	MHSC provides full-line securities services to corporations, financial institutions, public sector entities, and individuals.
	Others
	This segment consists of MHFG, its subsidiaries other than MHBK, MHTB, and MHSC, and its equity-method affiliates. They provide a wide range of customers with their various products and services such as those related to trust and custody, asset management, and private banking through companies such as TCSB, Mizuho Asset Management Co., Ltd., DIAM Co., Ltd. (an equity-method affiliate), and Mizuho Private Wealth Management Co., Ltd. This segment also provides non-banking services, including research and consulting services through Mizuho Research Institute Ltd., information technology-related services through Mizuho Information & Research Institute, Inc., and advisory services to financial institutions through Mizuho Financial Strategy Co., Ltd.
	The information below for reportable segments is derived from the internal management reporting systems. Management does not use information on segments’ assets to allocate resources and assess performance and has not prepared information on segment assets. Accordingly, information on segment assets is not available.
			The former MHBK (Consolidated)
						The former MHBK (Non-consolidated)																		The former			Others
																								MHIS
																								(Consolidated)
	2012(1)		Total			Total			Personal			Retail			Corporate		Corporate		Financial		Trading			(g)			(h)
									Banking			Banking			Banking		Banking		Institution		and
									(a)			(b)			(Large		(d)		& Public		others
															Corporations)				Sector		(f)
															(c)				Business
																			(e)
			(in billions of yen)
	Gross profits:
	Net interest income (expense)			583.9			545.4			224.3			95.1			17.8		118.6		22.2		67.4			0.7			37.8
	Net noninterest income			305.8			253.3			32.1			41			19		68.2		8.6		84.4			43.9			8.6
	Total			889.7			798.7			256.4			136.1			36.8		186.8		30.8		151.8			44.6			46.4
	General and administrative			608.5			556.4			218.6			108.2			18.5		86.4		14.5		110.2			40.9			11.2
	expenses
	Others			(14.0	)		—			—			—			—		—		—		—			—			(14.0	)
	Net business profits (losses)			267.2			242.3			37.8			27.9			18.3		100.4		16.3		41.6			3.7			21.2
			The former MHCB (Consolidated)																								MHTB			Others			MHFG
																											(Consolidated)						(Consolidated)
						The former MHCB (Non-consolidated)															The former			Others
																					MHSC
																					(Consolidated)
	2012(1)		Total			Total			Corporate			Corporate			Financial		Inter-		Trading		(n)			(o)			(p)			(q)			Total
									Banking			Banking			Institution		national		and
									(Large			(j)			& Public		Banking		others
									Corporations)						Sector		(l)		(m)
									(i)						Business
															(k)
	(in billions of yen)
	Gross profits:
	Net interest income (expense)			468.3			395			150.6			2.7			18.1		90.3		133.3		(8.1	)		81.4			42.5			(6.4	)		1,088.30
	Net noninterest income			449.4			286.8			114.4			1.1			15.8		86.9		68.6		151.7			10.9			104.8			54.8			914.8
	Total			917.7			681.8			265			3.8			33.9		177.2		201.9		143.6			92.3			147.3			48.4			2,003.10
	General and administrative			465.4			244.9			75.6			1.3			11.6		60.3		96.1		192.9			27.6			92.3			40.1			1,206.30
expenses
Others			(52.1	)		—			—			—			—		—		—		(0.1	)		(52.0	)		(3.7	)		(7.9	)		(77.7	)
Net business profits (losses)			400.2			436.9			189.4			2.5			22.3		116.9		105.8		(49.4	)		12.7			51.3			0.4			719.1
		The former MHBK (Consolidated)
					The former MHBK (Non-consolidated)																		Others
2013(1)(2)(4)		Total			Total			Personal			Retail			Corporate		Corporate		Financial		Trading			(g)
								Banking			Banking			Banking		Banking		Institution		and
								(a)			(b)			(Large		(d)		& Public		others
														Corporations)				Sector		(f)
														(c)				Business
																		(e)
		(in billions of yen)
Gross profits:
Net interest income (expense)			550.6			513.8			219.2			83.3			14.9		106.1		19.9		70.4			36.8
Net noninterest income			360.3			313.7			33.9			42.3			19.3		70.7		11		136.5			46.6
Total			910.9			827.5			253.1			125.6			34.2		176.8		30.9		206.9			83.4
General and administrative			568.2			524.4			218.6			113.7			11.6		73.2		14.3		93			43.8
expenses
Others			(7.4	)		—			—			—			—		—		—		—			(7.4	)
Net business profits (losses)			335.3			303.1			34.5			11.9			22.6		103.6		16.6		113.9			32.2
2013(1)(2)(4)		The former MHCB (Consolidated)																								MHTB			Others			MHFG
																										(Consolidated)						(Consolidated)
					The former MHCB (Non-consolidated)															MHSC			Others
																				(Consolidated)
		Total			Total			Corporate			Corporate			Financial		Inter-		Trading		(m)			(n)			(o)			(p)			Total
								Banking			Banking			Institution		national		and
								(Large			(i)			& Public		Banking		others
								Corporations)						Sector		(k)		(l)
								(h)						Business
														(j)
(in billions of yen)
Gross profits:
Net interest income (expense)			486.1			401.7			140.9			0.5			16.3		108.2		135.8		(1.8	)		86.2			39.5			(0.3	)		1,075.90
Net noninterest income			572.8			333.4			103.3			0.2			13.2		104.7		112		229			10.4			105			57.7			1,095.80
Total			1,058.90			735.1			244.2			0.7			29.5		212.9		247.8		227.2			96.6			144.5			57.4			2,171.70
General and administrative			471.9			241.1			76.8			1.3			12.2		66.6		84.2		197.1			33.7			90.1			40.8			1,171.00
expenses
Others			(50.0	)		—			—			—			—		—		—		—			(50.0	)		(3.5	)		(27.6	)		(88.5	)
Net business profits (losses)			537			494			167.4			(0.6	)		17.3		146.3		163.6		30.1			12.9			50.9			(11.0	)		912.2
2014(1)(2)(3)(4)		MHBK (Consolidated)																											MHTB			MHSC			Others			MHFG
																													(Consolidated)			(Consolidated)						(Consolidated)
					MHBK (Non-consolidated)																					Others
		Total			Total			Personal			Retail			Corporate		Corporate		Financial		Inter-			Trading			(h)			(i)			(j)			(k)			Total
								Banking			Banking			Banking		Banking		Institution		national			and
								(a)			(b)			(Large		(d)		& Public		Banking			others
														Corporations)				Sector		(f)			(g)
														(c)				Business
																		(e)
(in billions of yen)
Gross profits:
Net interest income			933.8			800.1			165			59.8			170.2		77.9		30.7		128.9			167.6			133.7			40.2			2.9			131.4			1,108.30
Net noninterest income (expenses)			407.4			398.2			32.9			34.8			126.7		51.8		20.1		139.8			(7.9	)		9.2			108.1			283.9			127.6			927
Total			1,341.20			1,198.30			197.9			94.6			296.9		129.7		50.8		268.7			159.7			142.9			148.3			286.8			259			2,035.30
General and administrative			711.3			659			171.3			87.8			83.8		58.8		25.1		82.5			149.7			52.3			90.9			246.2			180.9			1,229.30
expenses
Others			(56.1	)		—			—			—			—		—		—		—			—			(56.1	)		(2.9	)		—			(2.7	)		(61.7	)
Net business profits			573.8			539.3			26.6			6.8			213.1		70.9		25.7		186.2			10			34.5			54.5			40.6			75.4			744.3
Notes:
-1	As for the fiscal year ended March 31, 2012, “Others (h)”, “Others (o)”, and “Others (q)” include elimination of transactions between consolidated subsidiaries. As for the fiscal year ended March 31, 2013, “Others (g)”, “Others (n)”, and “Others (p)” include elimination of transactions between consolidated subsidiaries. As for the fiscal year ended March 31, 2014, “Others (h)” and “Others (k)” include elimination of transactions between consolidated subsidiaries.
-2	Beginning on April 1, 2013, the MHFG Group moved to a new group operational structure and realigned the reportable segments to reflect the new organizational structure. In addition, new allocation methods have been applied to the calculation of “Gross profits” and “General and administrative expenses”. Figures for the fiscal year ended March 31, 2013 have been reclassified under the new allocation methods. The effect of the change of allocation methods is not significant.
-3	As for the fiscal year ended March 31, 2014, “MHBK (Non-consolidated)” represents the sum of the performance of the former MHCB for the first quarter and the new MHBK for the second, third, and fourth quarters, while “Others (h)” includes the performance of the former MHBK for the first quarter, in light of the merger of the former MHBK and the former MHCB conducted in July 2013.
-4	Beginning on April 1, 2013, MHSC was turned into a directly-held subsidiary of MHFG. As for the fiscal year ended March 31, 2013, “MHSC (Consolidated) (m)” represents the performance of the former MHSC for the first three quarters and the new MHSC for the fourth quarter, while “Others (g)” includes the performance of the former MHIS for the first three quarters. As for the fiscal year ended March 31, 2014, “MHSC (Consolidated) (j)” represents the performance of the new MHSC, in light of the merger of the former MHSC and the former MHIS conducted in January 2013.
Aggregation of MHBK and MHCB
2012		MHBK and MHCB
		Personal			Retail			Corporate			Corporate			Financial		International		Trading		Total
		Banking			Banking			Banking			Banking			Institution		Banking		and
		(a)			(b)			(Large			(d)			& Public		(f)		others
								Corporations)						Sector				(g)
								(c)						Business
														(e)
		(in billions of yen)
Gross profits:
Net interest income			224.3			95.1			168.4			121.3			40.3		90.3		200.7		940.4
Net noninterest income			32.1			41			133.4			69.3			24.4		86.9		153		540.1
Total			256.4			136.1			301.8			190.6			64.7		177.2		353.7		1,480.50
General and administrative expenses			218.6			108.2			94.1			87.7			26.1		60.3		206.3		801.3
Others			—			—			—			—			—		—		—		—
Net business profits			37.8			27.9			207.7			102.9			38.6		116.9		147.4		679.2
2013		MHBK and MHCB
		Personal			Retail			Corporate			Corporate			Financial		International		Trading		Total
		Banking			Banking			Banking			Banking			Institution		Banking		and
		(a)			(b)			(Large			(d)			& Public		(f)		others
								Corporations)						Sector				(g)
								(c)						Business
														(e)
		(in billions of yen)
Gross profits:
Net interest income			219.2			83.3			155.8			106.6			36.2		108.2		206.2		915.5
Net noninterest income			33.9			42.3			122.6			70.9			24.2		104.7		248.5		647.1
Total			253.1			125.6			278.4			177.5			60.4		212.9		454.7		1,562.60
General and administrative expenses			218.6			113.7			88.4			74.5			26.5		66.6		177.2		765.5
Others			—			—			—			—			—		—		—		—
Net business profits			34.5			11.9			190			103			33.9		146.3		277.5		797.1
2014		MHBK and MHCB
		Personal			Retail			Corporate			Corporate			Financial		International		Trading		Total
		Banking			Banking			Banking			Banking			Institution		Banking		and
		(a)			(b)			(Large			(d)			& Public		(f)		others
								Corporations)						Sector				(g)
								(c)						Business
														(e)
		(in billions of yen)
Gross profits:
Net interest income			218.5			80			172.7			103.3			35.4		128.9		185		923.8
Net noninterest income			41.6			45.3			131.4			64.7			22.3		139.8		15.2		460.3
Total			260.1			125.3			304.1			168			57.7		268.7		200.2		1,384.10
General and administrative expenses			226.4			116.7			87.2			77.7			29		82.5		171.6		791.1
Others			—			—			—			—			—		—		—		—
Net business profits			33.7			8.6			216.9			90.3			28.7		186.2		28.6		593
Note:	The former MHBK and the former MHCB merged on July 1, 2013. Figures for the fiscal years ended March 31, 2012 and 2013 represent the simple aggregation of the performance of the former MHBK and the former MHCB, and figures for the fiscal year ended March 31, 2014 represent the simple aggregation of the performance of the former MHBK and the former MHCB for the first quarter, and the new MHBK for the second, third, and fourth quarters. Beginning on April 1, 2013, the MHFG Group moved to a new group operational structure and realigned the reportable segments to reflect the new organizational structure. In addition, new allocation methods have been applied to the calculation of “Gross profits” and “General and administrative expenses”. Figures for the fiscal year ended March 31, 2013 have been reclassified under the new allocation methods.
Reconciliation
As explained above, the measurement base for the internal management reporting system and the income and expenses items covered are different from the accompanying consolidated statements of income. Therefore, it is impracticable to present reconciliations of all the business segments’ information, other than net business profits, to corresponding items in the accompanying consolidated statements of income. A reconciliation of total net business profits under the internal management reporting system for the fiscal years ended March 31, 2012, 2013, and 2014 presented above to Income before income tax expense shown on the consolidated statements of income is as follows:
		2012			2013			2014
		(in billions of yen)
Net business profits			719.1			912.2			744.3
U.S. GAAP adjustments			87.2			129.2			(325.4	)
(Provision) credit for loan losses			23			(139.9	)		126.2
Net gains (losses) related to equity investments			(90.5	)		28.2			178.7
Non-recurring personnel expense			(39.3	)		(23.5	)		(14.8	)
Gains on disposal of premises and equipment			19.9			12.4			10.5
(Provision) credit for losses on off-balance-sheet instruments			1.2			(4.6	)		(12.1	)
Others—net			(57.8	)		(28.8	)		18.9
Income before income tax expense			662.8			885.2			726.3

Foreign_activities

Foreign activities	12 Months Ended
	Mar. 31, 2014
Foreign activities	'
	32. Foreign activities
	The following table presents consolidated income statement and total assets information by major geographic area. Foreign activities are defined as business transactions that involve customers residing outside of Japan. However, as the MHFG Group’s operations are highly integrated globally, estimates and assumptions have been made for an allocation among the geographic areas.
			Japan		Americas		Europe		Asia/Oceania		Total
									excluding
									Japan,
									and others
			(in billions of yen)
	Fiscal year ended March 31, 2012:
	Total revenue (1)			1,965.70		251.3		132		178.2		2,527.20
	Total expenses (2)			1,561.20		104		102.9		96.3		1,864.40
	Income before income tax expense			404.5		147.3		29.1		81.9		662.8
	Net income			419.2		131.2		28.1		70.5		649
	Total assets at end of fiscal year			124,443.60		25,368.90		8,868.50		7,680.60		166,361.60
	Fiscal year ended March 31, 2013:
	Total revenue (1)			2,190.70		383.7		125.8		162.6		2,862.80
	Total expenses (2)			1,668.90		140.5		48.4		119.8		1,977.60
	Income before income tax expense			521.8		243.2		77.4		42.8		885.2
	Net income			524.7		252.3		75		29.2		881.2
	Total assets at end of fiscal year			126,768.80		31,168.80		10,591.20		10,218.20		178,747.00
	Fiscal year ended March 31, 2014:
	Total revenue (1)			1,783.90		349.9		152.9		218.9		2,505.60
	Total expenses (2)			1,397.30		144.6		96.3		141.1		1,779.30
	Income before income tax expense			386.6		205.3		56.6		77.8		726.3
	Net income			198.9		189.7		54		57.6		500.2
	Total assets at end of fiscal year			124,557.70		27,527.80		10,784.50		12,829.30		175,699.30
	Notes:
	-1	Total revenue is comprised of Interest and dividend income and Noninterest income.
	-2	Total expenses are comprised of Interest expense, Provision (credit) for loan losses and Noninterest expenses.

Mizuho_Financial_Group_Inc_par

Mizuho Financial Group, Inc., parent company	12 Months Ended
	Mar. 31, 2014
Mizuho Financial Group, Inc., parent company	'
	33. Mizuho Financial Group, Inc., parent company
	The following tables present the parent company only financial information of MHFG:
	Condensed balance sheets
		2013			2014
		(in millions of yen)
	Assets:
	Cash and due from banks		200			167
	Interest-bearing deposits in other banks		26,165			17,103
	Investments in subsidiaries and affiliated companies		6,962,630			7,501,486
	Other		152,351			210,622
	Total		7,141,346			7,729,378
	Liabilities and shareholders’ equity:
	Short-term borrowings		1,146,995			1,061,460
	Long-term debt		240,000			240,000
	Other liabilities		26,231			49,448
	Shareholders’ equity		5,728,120			6,378,470
	Total		7,141,346			7,729,378
	Condensed statements of income
		2012			2013			2014
		(in millions of yen)
	Income:
	Dividends from subsidiaries and affiliated companies		7,955			233,056			285,130
	Management fees from subsidiaries		29,747			28,835			31,146
	Other income		12,643			34,668			33,894
	Total		50,345			296,559			350,170
	Expenses:
	Operating expenses		21,260			21,075			22,592
	Interest expense		16,383			15,870			14,608
	Other expense		1,431			1,207			5,724
	Total		39,074			38,152			42,924
	Equity in undistributed net income of subsidiaries		645,308			617,565			191,865
	Income before income tax expense		656,579			875,972			499,111
	Income tax expense		190			560			627
	Net income		656,389			875,412			498,484
	Condensed statements of cash flows
		2012			2013			2014
		(in millions of yen)
	Cash flows from operating activities:
	Net income		656,389			875,412			498,484
	Adjustments and other		(644,977	)		(685,149	)		(222,940	)
	Net cash provided by operating activities		11,412			190,263			275,544
	Cash flows from investing activities:
	Payments for purchases of securities of subsidiaries		(212	)		—			—
	Net change in other investing activities		80			1,570			2,631
	Net cash provided by (used in) investing activities		(132	)		1,570			2,631
	Cash flows from financing activities:
	Net change in short-term borrowings		60,000			(40,000	)		(90,000	)
	Proceeds from issuance of common stock		146,499			—			—
	Purchases of treasury stock		(2,560	)		(7	)		(37,013	)
	Dividends paid		(215,937	)		(152,542	)		(152,163	)
	Net change in other financing activities		730			749			968
	Net cash used in financing activities		(11,268	)		(191,800	)		(278,208	)
	Net increase (decrease) in cash and due from banks		12			33			(33	)
	Cash and due from banks at beginning of fiscal year		155			167			200
	Cash and due from banks at end of fiscal year		167			200			167

Subsequent_events

Subsequent events	12 Months Ended
	Mar. 31, 2014
Subsequent events	'
	34. Subsequent events
	Redemption of preferred securities
	On June 30, 2014, preferred securities, issued by the MHFG Group’s overseas special purpose companies, were redeemed in full. These special purpose companies are not consolidated in accordance with ASC 810 since the Group is not the primary beneficiary. Thus, the redemption of preferred securities did not reduce Noncontrolling interests in consolidated subsidiaries, but reduced Long-term debt in the Group’s consolidated balance sheets. The following table describes the details of the redeemed preferred securities.
	Issuer	Aggregate		Reason for the redemption
		redemption amount
		(in millions)
	Mizuho Capital Investment (USD) 2 Limited		$850		Arrival of optional redemption date
	Mizuho Capital Investment (JPY) 5 Limited		Series A ¥139,500		Arrival of optional redemption date

Basis_of_presentation_and_summ1

Basis of presentation and summary of significant accounting policies (Policies)	12 Months Ended
	Mar. 31, 2014
Basis of presentation	'
	Basis of presentation
	Mizuho Financial Group, Inc. (“MHFG”) is a joint stock corporation with limited liability under the laws of Japan. MHFG, through its subsidiaries (“the MHFG Group”, or “the Group”), provides domestic and international financial services in Japan and other countries. MHFG’s subsidiaries are segmented on the basis of the nature of the financial products and services. Mizuho Bank, Ltd. (“MHBK”) is a banking subsidiary and offers a wide range of financial products and services mainly in relation to deposits, lending and exchange settlement to individuals, small and medium enterprises (“SMEs”), large corporations, financial institutions, public sector entities and foreign corporations, including foreign subsidiaries of Japanese corporations. Mizuho Trust & Banking Co., Ltd. (“MHTB”) is a trust bank subsidiary and offers mainly trust-related products and consulting services. Mizuho Securities Co., Ltd. (“MHSC”) is a securities and investment banking subsidiary and offers full-line securities services to corporations, financial institutions, public sector entities and individuals. Other major subsidiaries include Trust & Custody Services Bank, Ltd. (“TCSB”), Mizuho Capital Co., Ltd., and Mizuho Business Financial Center Co., Ltd. See Note 31 “Business segment information” for further discussion of the Group’s segment information.
	The accompanying consolidated financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (“U.S. GAAP”). The consolidated financial statements are stated in Japanese yen, the currency of the country in which MHFG is incorporated and principally operates.
	The accompanying consolidated financial statements include the accounts of MHFG and its subsidiaries. MHFG’s fiscal year ends on March 31 and fiscal year of certain subsidiaries ends on December 31. The necessary adjustments have been made to the consolidated financial statements if significant intercompany transactions took place during the three-months periods. When determining whether to consolidate investee entities, we performed a careful analysis of the facts and circumstances of a particular relationship among entities as well as ownership of voting shares. The consolidated financial statements also include the accounts of the VIEs for which MHFG or its subsidiaries have been determined to be the primary beneficiary under the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 810, “Consolidation” (“ASC 810”). All significant intercompany transactions and balances have been eliminated in consolidation. The MHFG Group accounts for investments in entities over which it has significant influence using the equity method of accounting. These investments are included in Other investments and the Group’s proportionate share of income or loss is included in Investment gains (losses)—net.
Use of estimates	'
	Use of estimates
	The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect reported amounts and related disclosures. Specific areas, among others, requiring the application of management’s estimates and judgment include assumptions pertaining to the allowance for loan losses, allowance for losses on off-balance-sheet instruments, deferred tax assets, derivative financial instruments, investments and pension and other employee benefits. Actual results could differ from estimates and assumptions made.
Definition of cash and due from banks	'
	Definition of cash and due from banks
	For purposes of the consolidated statements of cash flows, Cash and due from banks include cash on hand, cash items in the process of collection and noninterest-bearing deposits with banks.
Translation of foreign currency financial statements and foreign currency transactions	'
	Translation of foreign currency financial statements and foreign currency transactions
	Financial statements of overseas entities are prepared using the functional currency of each entity and translated into Japanese yen for consolidation purposes. Assets and liabilities are translated using the fiscal-year-end exchange rate of each functional currency, and income and expense using the average rate of each functional currency for the period.
	Foreign currency translation gains and losses related to the financial statements of overseas entities of the MHFG Group, net of related income tax effects, are credited or charged directly to Foreign currency translation adjustments, a component of Accumulated other comprehensive income (loss), net of tax (“AOCI”). The tax effects of gains and losses related to the foreign currency translation of financial statements of overseas entities are not recognized unless it is apparent that the temporary differences will reverse in the foreseeable future.
	Assets and liabilities denominated in foreign currencies are translated into Japanese yen at the fiscal-year-end foreign exchange rates, and gains and losses resulting from such translation are included in Foreign exchange gains (losses)—net, as appropriate. Foreign currency denominated income and expenses are translated using the average exchange rates for the period.
Call loans and call money	'
	Call loans and call money
	Call loans and call money represent lending/borrowing through the Japanese short-term money market to/from other financial institutions such as banks, insurance companies, and securities brokerage houses.
Repurchase and resale agreements, securities lending and borrowing and other secured financing transactions	'
	Repurchase and resale agreements, securities lending and borrowing and other secured financing transactions
	Securities sold under agreements to repurchase (“repurchase agreements”), securities purchased under agreements to resell (“resale agreements”) and securities lending and borrowing transactions are accounted for as secured financing or lending transactions when control over the underlying securities is not deemed to be surrendered by the transferor. Otherwise, they are recorded as sales of securities with related forward repurchase commitments or purchases of securities with related forward resale commitments in accordance with ASC 860, “Transfers and Servicing” (“ASC 860”).
	Repurchase transactions where the maturity of the security transferred as collateral matches the maturity of the repurchase agreements (“repo-to-maturity transactions”) are accounted for as sales rather than collateralized financings where the criteria for derecognition of the securities transferred under ASC 860 are met. There were no such transactions accounted for as sales as of March 31, 2013 and 2014.
	Under resale agreements, securities borrowing and certain derivatives transactions, the MHFG Group receives collateral in the form of securities. In many cases, the MHFG Group is permitted to sell or repledge the securities obtained as collateral. Disclosures of such collateral are presented in Note 8 “Pledged assets and collateral”. With respect to repurchase agreements, securities lending, and certain derivative transactions, counterparties may have the right to sell or repledge securities that the MHFG Group has pledged as collateral. The MHFG Group separately discloses these pledged securities in the consolidated balance sheets.
	The MHFG Group monitors credit exposure arising from resale agreements, repurchase agreements, securities borrowing and securities lending transactions on a daily basis, and additional collateral is obtained from or returned to counterparties, as appropriate.
Trading securities and trading securities sold, not yet purchased	'
	Trading securities and trading securities sold, not yet purchased
	Trading securities consist of securities and money market instruments that are bought and held principally for the purpose of reselling in the near term with the objective of generating profits on short-term fluctuations in price. Trading securities sold, not yet purchased, are securities and money market instruments sold to third parties that the MHFG Group does not own and is obligated to purchase at a later date to cover the short position. Trading securities and trading securities sold, not yet purchased, are recorded on the trade date. Trading securities and trading securities sold, not yet purchased, are recorded at fair value in the consolidated balance sheets in Trading account assets and Trading account liabilities with realized and unrealized gains and losses recorded on a trade date basis in Trading account gains (losses)—net in the consolidated statements of income. Interest and dividends on trading securities, including securities sold, not yet purchased, are recorded in Interest and dividend income or Interest expense on an accrual basis.
Investments	'
	Investments
	Debt securities that the MHFG Group has both the positive intent and ability to hold to maturity are classified as Held-to-maturity securities and carried at amortized cost. Debt securities that the MHFG Group may not hold to maturity and any marketable equity securities, other than those classified as trading securities, are classified as Available-for-sale securities, and are carried at fair value, with unrealized gains and losses reported in AOCI.
	The credit component of an other-than-temporary impairment of a debt security is reported in Investment gains (losses)—net and the noncredit component is reported in Other comprehensive income (loss). See Note 3 “Investments” for further discussion of impairment. Interest and dividends, as well as amortization of premiums and accretion of discounts, are reported in Interest and dividend income. Amortization of premiums and accretion of discounts on debt securities are recognized over the remaining maturity under the interest method. Gains and losses on disposition of investments are computed using the first-in first-out method for debt securities and the average method for equity securities, and are recorded on the trade date.
	Other investments include marketable and non-marketable equity securities accounted for using the equity method, marketable and non-marketable investments held by consolidated investment companies carried at fair value under specialized industry accounting principles for investment companies, and other non-marketable equity securities carried at cost, less other-than-temporary impairment, if any.
Derivative financial instruments	'
	Derivative financial instruments
	Derivative financial instruments are bought and held principally for the purpose of market making for customers, proprietary trading in order to generate trading revenues and fee income, and also to manage the MHFG Group’s exposure to interest rate, credit and market risks related to asset and liability management. Such derivative financial instruments include interest rate, foreign currency, equity, commodity and credit default swap agreements, options, caps and floors, and financial futures and forward contracts.
	Derivatives bought and held for trading purposes are recorded in the consolidated balance sheets at fair value in Trading account assets and Trading account liabilities. The fair value of derivatives in a gain position and a loss position are reported as Trading account assets and Trading account liabilities, respectively.
	Derivatives used for asset and liability management include contracts that qualify for hedge accounting under ASC 815, “Derivatives and Hedging” (“ASC 815”). To be eligible for hedge accounting, derivative instruments must be highly effective in achieving offsetting changes in fair values or variable cash flows of the hedged items attributable to the particular risk being hedged. All qualifying hedging derivatives are valued at fair value and included in Trading account assets or Trading account liabilities. Derivatives that do not qualify for hedge accounting under ASC 815 are treated as trading positions and are accounted for as such. The fair value amounts recognized for such derivatives are not offset against the amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral under master netting agreement with the same counterparty.
	The fair value of derivative financial instruments is determined based on quoted market prices or broker-dealer quotes, if available. If not, the fair value is estimated using quoted market prices for similar instruments, option or binomial pricing models or a present value cash flow analysis, utilizing current observable market information, where available. In determining the fair value, the Group considers various factors such as exchange or over-the-counter market quotes, time value of money and volatility factors for options and warrants, observed prices for similar or synthetic instruments, and counterparty credit quality including potential exposure.
	Changes in the fair value of all derivatives are recorded in earnings, except for derivatives qualifying as net investment hedges under ASC 815 which are recorded in AOCI. The changes in the fair values of all derivatives relating to foreign currency exchange rates are included in Foreign exchange gains (losses)—net and Trading account gains (losses)—net. Other elements of the changes in the fair values, including interest rate, equity and credit related components except that of certain credit derivatives hedging the credit risk in the corporate loan portfolio, are recognized in Trading account gains (losses)—net. The net gain (loss) resulting from changes in the fair values of certain credit derivatives where the Group purchases protection to mitigate its credit risk exposure related to its corporate loan portfolio is recorded in Other noninterest income (expenses).
	Certain financial and hybrid instruments often contain embedded derivative instruments that possess implicit or explicit contract terms similar to those of a derivative instrument. Such derivative instruments are required to be fair-valued separately from the host contracts if they meet the bifurcation criteria of an embedded derivative. Such criteria include whether the entire instrument is not marked to market through earnings, the economic characteristics and risks of the embedded contract terms are not clearly and closely related to those of the host contract and the embedded contract terms would meet the definition of a derivative on a stand-alone basis.
Loans	'
	Loans
	Loans are generally carried at the principal amount adjusted for unearned income and deferred net nonrefundable loan fees and costs. Loan origination fees, net of certain direct origination costs are deferred and recognized over the contractual life of the loan as an adjustment of yield using a method that approximates the interest method. Interest income on performing loans is accrued and credited to income as it is earned. Unearned income and discounts or premiums on purchased loans are deferred and recognized over the life of the loan using a method that approximates the interest method.
	Loans are considered impaired when, based on current information and events, it is probable that the MHFG Group will be unable to collect all the scheduled payments of principal and interest when due according to the contractual terms of the loan. Factors considered by management in determining if a loan is impaired include delinquency status and the ability of the debtor to make payment of the principal and interest when due. Impaired loans include loans past due for 90 days or more and restructured loans that meet the definition of troubled debt restructuring (“TDR”) in accordance with ASC 310 “Receivables” (“ASC 310”).
	All of the MHFG Group’s impaired loans are designated as nonaccrual loans and thus interest accrual and amortization of net origination fees are suspended and capitalized interest is written off. Cash received on nonaccrual loans is accounted for as reduction of the loan principal if the ultimate collectibility of the principal amount is uncertain, otherwise, as interest income. Loans are not restored to accrual status until interest and principal payments are current and future payments are reasonably assured. Impaired loans return to non-impaired loans and accrual status, when the MHFG Group determines that the borrower poses no problems regarding current certainty of debt fulfillment. In general, such determination is made if the borrower qualifies for an obligor rating of E2 or above and is not classified as a special attention obligor. With respect to loans restructured in TDR, in general, such loans return to non-impaired loans, and accrual status, when the borrower qualifies for an obligor rating of D or above. See Note 4 “Loans” for the definitions of obligor ratings.
	Loans that have been identified to be sold are classified as loans held for sale within Other assets and are accounted for at the lower of cost or fair value on an individual loan basis. If management decides to retain certain loans held for sale for the foreseeable future or until maturity or payoff, such items are transferred to Loans at the lower of cost or fair value.
Securitization	'
	Securitization
	The MHFG Group engages in securitization activities related to mortgage loans and other loans in the normal course of business. The MHFG Group records a loan securitization as a sale when the transferred loans are legally isolated from the Group’s creditors and the accounting criteria for a sale are met in accordance with ASC 860. Otherwise, the transfer is accounted for as a collateralized borrowing.
Allowance and provision (credit) for loan losses	'
	Allowance and provision (credit) for loan losses
	The MHFG Group maintains an appropriate amount of allowance for loan losses to absorb probable losses inherent in the loan portfolio and makes adjustments to such allowance through the Provision (credit) for loan losses in the consolidated statements of income. Loan principal that management judges to be uncollectible, based on detailed loan reviews and a credit quality assessment, is charged off against the allowance for loan losses. In general, the MHFG Group charges off loans when the Group determines that the debtor should be classified as substantially bankrupt or bankrupt. See Note 4 “Loans” for the definitions of obligor categories. Obligors classified in the retail portfolio segment are generally determined to be substantially bankrupt when they are past due for more than six months, and as for other obligors, the Group separately monitors the credit quality of each obligor without using time-based triggers. Subsequent recoveries of previously charged-off loan balances are recorded as an increase to the allowance for loan losses as the recoveries are received.
	The credit quality review process and the credit rating process serve as the basis for determining the allowance for loan losses. Through such processes loans are categorized into groups to reflect the probability of default, whereby the MHFG Group’s management assesses the ability of borrowers to service their debt, taking into consideration current financial information, ability to generate cash, historical payment experience, analysis of relevant industry segments and current trends. In determining the appropriate level of the allowance, the MHFG Group evaluates the probable loss by category of loan based on its risk type and characteristics.
	The allowance for loan losses is determined in accordance with ASC 310 and ASC 450, “Contingencies” (“ASC 450”). The MHFG Group measures the impairment of a loan when it is probable that the Group will be unable to collect all amounts due according to the contractual terms of the loan agreement, based on (1) the present value of expected future cash flows, after considering the restructuring effect and subsequent payment default with respect to TDRs, discounted at the loan’s initial effective interest rate, (2) the loan’s observable market price, or (3) the fair value of the collateral if the loan is collateral dependent. The collateral that the Group obtains for loans consists primarily of real estate or listed securities. In obtaining the collateral, the Group evaluates the fair value of the collateral and its legal enforceability. The Group also conducts subsequent re-evaluations at least once a year. As it pertains to real estate, valuation is generally conducted by an appraising subsidiary which is independent from the Group’s loan origination sections by using generally accepted valuation techniques such as (1) the replacement cost approach, (2) the sales comparison approach or (3) the income approach. In the case of large real estate collateral, the Group generally retains third-party appraisers to conduct the valuation. As to listed securities, observable market prices are used for valuation.
	The formula allowance is applied to groups of small balance, homogeneous loans that are collectively evaluated for impairment and for non-homogeneous loans that have not been identified as impaired. The evaluation of inherent loss in respect of these loans involves a high degree of uncertainty, subjectivity and judgment because probable loan losses are not easily identifiable or measurable. In determining the formula allowance, the MHFG Group relies on a statistical analysis that incorporates loss rates based on its own historical loss experience and third party data such as the number of corporate default cases which is updated once a year. In determining the allowance amount, the Group analyzes (1) the probability of default: (a) through the most recently available data for the past six years, in the case of normal obligors; and (b) through the most recently available data since April 2002, in the case of watch obligors; and (2) the loss given default through the most recently available data for the past six years. As it pertains to TDR loans in the retail portfolio segment, which are subject to collective evaluation for impairment, the restructuring itself, as well as subsequent payment default, if any, are considered in determining obligor ratings.
	The historical loss rate is adjusted, where appropriate, to reflect current factors, such as general economic and business conditions affecting the key lending areas of the MHFG Group, credit quality trends, specific industry conditions within portfolio segments, and recent loss experience in particular segments of the portfolio. The estimation of the formula allowance is back-tested on a periodic basis by comparing the allowance with the actual results subsequent to the balance sheet date.
Allowance and provision (credit) for losses on off-balance-sheet instruments	'
	Allowance and provision (credit) for losses on off-balance-sheet instruments
	The MHFG Group maintains an allowance for losses on off-balance-sheet credit instruments, such as guarantees, standby letters of credit, commitments to invest in securities and commitments to extend credit, in the same manner as the allowance for loan losses. The allowance is recorded in Other liabilities. Net changes in the allowance for losses on off-balance-sheet instruments are accounted for in the Provision (credit) for losses on off-balance-sheet instruments in the consolidated statements of income.
Premises and equipment	'
	Premises and equipment
	Premises and equipment are stated at historical cost, and depreciation and amortization are recorded over the estimated useful lives of the assets, except for leasehold improvements, which are amortized over the shorter of the estimated useful lives of the assets or the lease term. Depreciation and amortization are principally computed in accordance with the straight-line method with respect to buildings and leasehold improvements and in accordance with the declining-balance method with respect to other premises and equipment.
	The useful lives of premises and equipment are as follows:
		Years
	Buildings		3 to 50
	Equipment and furniture		2 to 20
	Leasehold improvements		2 to 50
	Regular repairs and maintenance costs that do not extend the estimated useful life of an asset are charged to expense as incurred. Upon sale or disposition of premises and equipment, the cost and related accumulated depreciation or amortization are removed from the accounts, and any gains or losses on disposal are included in Gains on disposal of premises and equipment or Occupancy expenses.
Impairment of long-lived assets	'
	Impairment of long-lived assets
	The MHFG Group’s long-lived assets that are held for use are reviewed periodically for events or changes in circumstances that indicate possible impairment. The Group’s impairment review is based on an undiscounted cash flow analysis of a group of assets, combined with associated liabilities, at the lowest level for which identifiable cash flows exist. Impairment occurs when the carrying value of the asset group exceeds the future undiscounted cash flows that the asset group is expected to generate. When impairment is identified, the future cash flows are then discounted to determine the estimated fair value of the asset group and an impairment charge is recorded for the difference between the carrying value and the estimated fair value of the asset group. The long-lived assets to be disposed of by sale are carried at the lower of the carrying amount or fair value, less estimated cost to sell.
Software	'
	Software
	Internal and external costs incurred in connection with developing and obtaining software for internal use that occur during the application development stage are capitalized. Such costs include salaries and benefits for employees directly involved with and who devote time to the project, to the extent such time is incurred directly on the internal use software project. The capitalization of software ceases when the software project has been substantially completed. The capitalized software is amortized on a straight-line basis over the estimated useful life, generally 5 to 10 years. Internal use software is reviewed for impairment when triggering events occur.
Goodwill	'
	Goodwill
	Goodwill represents the excess of the total fair value of the acquired company, which consists of the consideration transferred, the fair value of any interest in the acquiree already held by the acquirer and the fair value of any noncontrolling interest in the acquiree over the fair value of net identifiable assets acquired at the date of acquisition in a business combination. The MHFG Group accounts for goodwill in accordance with ASC 350, “Intangibles—Goodwill and Other” (“ASC 350”). Goodwill is recorded at a designated reporting unit level for the purpose of assessing impairment. An impairment loss is recorded to the extent the carrying amount of goodwill exceeds its estimated fair value.
Intangible assets	'
	Intangible assets
	Intangible assets having definite useful lives are amortized over their estimated useful lives on either a straight-line basis or the method that reflects the pattern in which the economic benefits of the intangible assets are consumed. Intangible assets acquired by the merger of MHSC and Shinko Securities Co., Ltd. (“Shinko”) consist primarily of customer relationship intangibles, and are amortized over a weighted-average amortization period of 16 years. Intangible assets having indefinite useful lives are not amortized and are subject to impairment tests. An impairment loss is recorded to the extent the carrying amount of indefinite-lived intangible asset exceeds its estimated fair value. For intangible assets subject to amortization, an impairment loss is recorded if the carrying amount is not recoverable and exceeds its estimated fair value.
Pension and other employee benefits	'
	Pension and other employee benefits
	MHFG and certain subsidiaries sponsor severance indemnities and pension plans, which provide defined benefits to retired employees. Periodic expense and accrued liabilities are computed based on the actuarial present value of benefits, net of investment returns expected from plan assets and their fair values at the balance sheet date. Net periodic expense is charged to Salaries and employee benefits.
Stock-based compensation	'
	Stock-based compensation
	The compensation cost associated with stock compensation-type stock options is measured at fair value using the Black-Scholes option pricing model.
Long-term debt	'
	Long-term debt
	Premiums, discounts and issuance costs of long-term debt are amortized based on a method that approximates the interest method over the respective terms of the long-term debt.
Obligations under guarantees	'
	Obligations under guarantees
	The MHFG Group provides customers with a variety of guarantees and similar arrangements, including standby letters of credit, financial and performance guarantees, credit protections, and liquidity facilities. The MHFG Group recognizes guarantee fee income over the guarantee period. The MHFG Group receives such a guarantee fee at the inception of the guarantee or in installments and, in either case, the present value of the total fees approximates the fair value of the guarantee.
Fair Value Measurements	'
	Fair Value Measurements
	The MHFG Group carries certain of its financial assets and liabilities at fair value on a recurring basis. These financial assets and liabilities are primarily composed of trading account assets, trading account liabilities and available-for-sale securities. In addition, the Group measures certain financial assets and liabilities, at fair value on a non-recurring basis. Those assets and liabilities primarily include items that are measured at the lower of cost or fair value such as loans held for sale, and items that were initially measured at cost and have been written down to fair value due to impairments, such as loans and other investments.
	Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. In accordance with ASC 820, “Fair Value Measurement” (“ASC 820”), the Group classifies its financial assets and liabilities into the fair value hierarchy (Level 1, 2, and 3). See Note 28 “Fair value” for the detailed definition of each level.
	When determining fair value, the MHFG Group considers the principal or most advantageous market in which the Group would transact and considers assumptions that market participants would use when pricing the asset or liability. The Group maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. See Note 28 “Fair value” for descriptions of valuation methodologies used for its assets and liabilities by product.
Fees and commissions	'
	Fees and commissions
	Fee revenue is recognized when all of the following criteria have been met: persuasive evidence of an agreement exists, services have been rendered, the price is fixed or determinable, and collectibility is reasonably assured. Fees on securities-related business and fees on funds transfer and collection services are generally recognized as revenue when the related services are performed. Fees on credit-related business, excluding loan origination fees to be deferred and recognized over the loan period as an adjustment of yield, are generally recognized either at one time when the service is rendered or over the related transaction period. Fees and commissions are presented on a gross basis and exclusive of consumption taxes.
Income taxes	'
	Income taxes
	Income taxes are accounted for in accordance with ASC 740, “Income Taxes” (“ASC 740”). Deferred income taxes reflect the net tax effects of (1) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the corresponding amounts used for income tax purposes, and (2) operating loss and tax credit carryforwards. A valuation allowance is recorded for any portion of the deferred tax assets unless it is more likely than not that the deferred tax assets will be realized. Deferred income tax benefit or expense is recognized for the changes in the net deferred tax asset or liability between periods.
Earnings per common share	'
	Earnings per common share
	Basic earnings per common share are computed by dividing net income attributable to MHFG common shareholders by the weighted average number of common shares outstanding during the fiscal year. Diluted earnings per common share reflect the possible exercise of all convertible securities, such as convertible preferred stock to the extent they are not anti-dilutive. See Note 18 “Earnings per common share” for the computation of basic and diluted earnings per common share.

Basis_of_presentation_and_summ2

Basis of presentation and summary of significant accounting policies (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule Of Useful Lives For Property Plant Equipment	'
	The useful lives of premises and equipment are as follows:
		Years
	Buildings		3 to 50
	Equipment and furniture		2 to 20
	Leasehold improvements		2 to 50

Investments_Tables

Investments (Tables)	12 Months Ended
	Mar. 31, 2014
Amortized Cost Gross Unrealized Gains and Losses and Fair Value of Investments Table	'
	The amortized cost, gross unrealized gains and losses, and fair value of available-for-sale and held-to-maturity securities at March 31, 2013 and 2014 are as follows:
			Amortized cost		Gross unrealized		Gross unrealized		Fair value
					gains		losses
			(in millions of yen)
	2013
	Available-for-sale securities:
	Debt securities:
	Japanese government bonds			30,709,499		79,378		5,677		30,783,200
	Japanese local government bonds			239,695		4,109		47		243,757
	U.S. Treasury bonds and federal agency securities			177,438		623		36		178,025
	Other foreign government bonds			596,305		1,914		94		598,125
	Agency mortgage-backed securities (1)			986,646		20,496		1,429		1,005,713
	Residential mortgage-backed securities			430,325		13,889		2,131		442,083
	Commercial mortgage-backed securities			246,169		7,487		3,528		250,128
	Japanese corporate bonds and other debt securities (2)			2,197,270		22,582		5,288		2,214,564
	Foreign corporate bonds and other debt securities (3)			542,958		17,768		1,803		558,923
	Equity securities (marketable)			1,699,475		1,440,102		144		3,139,433
	Total			37,825,780		1,608,348		20,177		39,413,951
	Held-to-maturity securities:
	Debt securities:
	Japanese government bonds			3,000,403		20,023		82		3,020,344
	Total			3,000,403		20,023		82		3,020,344
	2014
	Available-for-sale securities:
	Debt securities:
	Japanese government bonds			22,039,640		20,063		3,727		22,055,976
	Japanese local government bonds			241,985		2,783		106		244,662
	U.S. Treasury bonds and federal agency securities			158,344		434		4,297		154,481
	Other foreign government bonds			719,281		2,356		455		721,182
	Agency mortgage-backed securities (1)			955,291		13,288		7,705		960,874
	Residential mortgage-backed securities			318,955		14,757		1,707		332,005
	Commercial mortgage-backed securities			159,289		3,032		1,417		160,904
	Japanese corporate bonds and other debt securities (2)			2,015,045		16,316		3,284		2,028,077
	Foreign corporate bonds and other debt securities (3)			559,947		10,755		2,193		568,509
	Equity securities (marketable)			1,667,669		1,761,025		6,603		3,422,091
	Total			28,835,446		1,844,809		31,494		30,648,761
	Held-to-maturity securities:
	Debt securities:
	Japanese government bonds			4,040,083		17,954		220		4,057,817
	Total			4,040,083		17,954		220		4,057,817
	Notes	:
	-1	Agency mortgage-backed securities presented in the above table consist of U.S. agency securities and Japanese agency securities, of which the fair values were ¥143,954 million and ¥861,759 million, respectively, at March 31, 2013, and ¥105,553 million and ¥855,321 million, respectively, at March 31, 2014. U.S. agency securities primarily consist of Government National Mortgage Association or Ginnie Mae securities, which are guaranteed by the United States government. All Japanese agency securities are mortgage-backed securities issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise.
	-2	Other debt securities presented in the above table primarily consist of certificates of deposit (“CDs”) and asset-backed securities (“ABS”), of which the total fair values were ¥185,497 million at March 31,2013, and ¥214,488 million at March 31, 2014.
	-3	Other debt securities presented in the above table primarily consist of CDs, ABS, and collateral loan obligations (“CLO”), of which the total fair values were ¥243,633 million at March 31,2013, and ¥178,055 million at March 31, 2014.
Investments Classified by Contractual Maturity Date	'
	Securities not due at a single maturity date and securities embedded with call or prepayment options, such as mortgage-backed securities, are included in the table below based on their contractual maturities.
	Amortized cost		Due in one		Due after one		Due after five		Due after		Total
			year or less		year through		years through		ten years
					five years		ten years
			(in millions of yen)
	Available-for-sale securities:
	Debt securities:
	Japanese government bonds			5,926,354		13,876,023		2,237,263		—		22,039,640
	Japanese local government bonds			30,346		130,751		80,108		780		241,985
	U.S. Treasury bonds and federal agency securities			43,475		75,005		39,864		—		158,344
	Other foreign government bonds			507,140		211,949		—		192		719,281
	Agency mortgage-backed securities			—		—		—		955,291		955,291
	Residential mortgage-backed securities			—		—		—		318,955		318,955
	Commercial mortgage-backed securities			4,085		123,455		31,749		—		159,289
	Japanese corporate bonds and other debt securities			369,682		1,131,664		326,861		186,838		2,015,045
	Foreign corporate bonds and other debt securities			221,916		251,536		83,865		2,630		559,947
	Total			7,102,998		15,800,383		2,799,710		1,464,686		27,167,777
	Held-to-maturity securities:
	Debt securities:
	Japanese government bonds			600,047		3,080,346		359,690		—		4,040,083
	Total			600,047		3,080,346		359,690		—		4,040,083
	Fair value		Due in one		Due after one		Due after five		Due after		Total
			year or less		year through		years through		ten years
					five years		ten years
			(in millions of yen)
	Available-for-sale securities:
	Debt securities:
	Japanese government bonds			5,926,642		13,882,371		2,246,963		—		22,055,976
	Japanese local government bonds			30,384		131,438		81,952		888		244,662
	U.S. Treasury bonds and federal agency securities			43,907		72,142		38,432		—		154,481
	Other foreign government bonds			507,577		213,355		—		250		721,182
	Agency mortgage-backed securities			—		—		—		960,874		960,874
	Residential mortgage-backed securities			—		—		—		332,005		332,005
	Commercial mortgage-backed securities			4,087		124,981		31,836		—		160,904
	Japanese corporate bonds and other debt securities			370,157		1,137,145		329,033		191,742		2,028,077
	Foreign corporate bonds and other debt securities			222,527		253,142		89,625		3,215		568,509
	Total			7,105,281		15,814,574		2,817,841		1,488,974		27,226,670
	Held-to-maturity securities:
	Debt securities:
	Japanese government bonds			601,750		3,091,769		364,298		—		4,057,817
	Total			601,750		3,091,769		364,298		—		4,057,817
Unrealized Loss Position Investments	'
	The following tables show the gross unrealized losses and fair value of available-for-sale and held-to-maturity securities, aggregated by the length of time that individual securities have been in a continuous unrealized loss position, at March 31, 2013 and 2014:
			Less than 12 months				12 months or more				Total
			Fair		Gross		Fair		Gross		Fair		Gross
			value		unrealized		value		unrealized		value		unrealized
					losses				losses				losses
			(in millions of yen)
	2013
	Available-for-sale securities:
	Debt securities:
	Japanese government bonds			5,059,495		1,520		406,684		4,157		5,466,179		5,677
	Japanese local government bonds			27,243		47		—		—		27,243		47
	U.S. Treasury bonds and federal agency securities			69,168		36		—		—		69,168		36
	Other foreign government bonds			207,942		94		—		—		207,942		94
	Agency mortgage-backed securities (1)			90,832		1,429		—		—		90,832		1,429
	Residential mortgage-backed securities			12,778		9		122,363		2,122		135,141		2,131
	Commercial mortgage-backed securities			7,159		111		122,588		3,417		129,747		3,528
	Japanese corporate bonds and other debt securities			88,146		333		222,516		4,955		310,662		5,288
	Foreign corporate bonds and other debt securities			54,599		114		65,417		1,689		120,016		1,803
	Equity securities (marketable)			8,488		128		699		16		9,187		144
	Total			5,625,850		3,821		940,267		16,356		6,566,117		20,177
	Held-to-maturity securities:
	Debt securities:
	Japanese government bonds			199,730		82		—		—		199,730		82
	Total			199,730		82		—		—		199,730		82
	2014
	Available-for-sale securities:
	Debt securities:
	Japanese government bonds			10,526,182		2,871		880,520		856		11,406,702		3,727
	Japanese local government bonds			48,471		90		12,730		16		61,201		106
	U.S. Treasury bonds and federal agency securities			66,865		2,865		38,432		1,432		105,297		4,297
	Other foreign government bonds			203,026		275		7,654		180		210,680		455
	Agency mortgage-backed securities (2)			102,904		2,348		76,369		5,357		179,273		7,705
	Residential mortgage-backed securities			9,771		137		78,938		1,570		88,709		1,707
	Commercial mortgage-backed securities			11,133		117		43,170		1,300		54,303		1,417
	Japanese corporate bonds and other debt securities			130,020		359		60,230		2,925		190,250		3,284
	Foreign corporate bonds and other debt securities			122,563		1,846		33,960		347		156,523		2,193
	Equity securities (marketable)			132,590		6,603		10		—		132,600		6,603
	Total			11,353,525		17,511		1,232,013		13,983		12,585,538		31,494
	Held-to-maturity securities:
	Debt securities:
	Japanese government bonds			9,962		40		199,670		180		209,632		220
	Total			9,962		40		199,670		180		209,632		220
	Notes	:
	-1	Agency mortgage-backed securities presented in the above table represent U.S. agency securities. U.S. agency securities primarily consist of Government National Mortgage Association or Ginnie Mae securities, which are guaranteed by the United States government.
	-2	Agency mortgage-backed securities presented in the above table consist of U.S. agency securities and Japanese agency securities, of which the fair values were ¥105,208 million and ¥74,065 million, respectively, at March 31, 2014. All Japanese agency securities are mortgage-backed securities issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise.
Other Investments Disclosure	'
	The following table summarizes the composition of Other investments:
			2013		2014
			(in millions of yen)
	Equity method investments			225,696		196,015
	Investments held by consolidated investment companies			75,780		70,599
	Other equity interests			536,659		526,075
	Total			838,135		792,689

Loans_Tables

Loans (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Accounts, Notes, Loans and Financing Receivable	'
	The table below presents loans outstanding by domicile and industry of borrower at March 31, 2013 and 2014:
			2013		2014
			(in millions of yen)
	Domestic:
	Manufacturing			8,078,871		8,025,932
	Construction and real estate			7,477,853		7,204,594
	Services			3,972,011		3,956,742
	Wholesale and retail			5,355,974		5,350,707
	Transportation and communications			3,147,106		3,247,394
	Banks and other financial institutions			3,142,998		3,460,147
	Government and public institutions			6,907,426		6,734,451
	Other industries (Note)			4,521,994		4,983,821
	Individuals:
	Mortgage loans			11,234,561		11,187,206
	Other			741,519		787,313
	Total domestic			54,580,313		54,938,307
	Foreign:
	Commercial and industrial			10,481,071		12,937,005
	Banks and other financial institutions			4,088,651		4,610,141
	Government and public institutions			595,911		883,004
	Other (Note)			199,518		255,083
	Total foreign			15,365,151		18,685,233
	Total			69,945,464		73,623,540
	Less: Unearned income and deferred loan fees—net			111,981		138,586
	Total loans before allowance for loan losses			69,833,483		73,484,954
	Note:	Other industries of domestic and Other of foreign include trade receivables and lease receivables of consolidated VIEs.
Financing Receivable Credit Quality Indicators	'
	The table below presents credit quality information of loans based on the MHFG Group’s internal rating system at March 31, 2013 and 2014:
			Normal obligors								Watch obligors excluding						Impaired		Total
											special attention obligors (1)						loans
			A-B		C-D		Retail (2)		Other (3)		E1-E2		Retail (2)		Other (3)
			(in millions of yen)
	2013
	Domestic:
	Manufacturing			4,171,212		2,615,406		119,183		307,946		498,638		22,569		8,013		335,904		8,078,871
	Construction and real estate			2,524,644		3,486,850		659,844		148,893		387,254		20,671		664		249,033		7,477,853
	Services			1,736,931		1,734,482		219,089		4,035		160,754		26,621		—		90,099		3,972,011
	Wholesale and retail			1,853,573		2,699,053		261,322		83,065		236,545		49,710		11		172,695		5,355,974
	Transportation and communications			2,236,404		685,237		94,233		350		59,573		12,274		—		59,035		3,147,106
	Banks and other financial institutions			2,246,804		666,197		2,172		5,311		208,510		221		—		13,783		3,142,998
	Government and public institutions			6,797,133		11,729		—		98,564		—		—		—		—		6,907,426
	Other industries			1,620,061		743,214		3,341		2,058,974		13,044		448		77,548		5,364		4,521,994
	Individuals			—		191,360		11,219,209		170,768		33,618		121,468		4,032		235,625		11,976,080
	Total domestic			23,186,762		12,833,528		12,578,393		2,877,906		1,597,936		253,982		90,268		1,161,538		54,580,313
	Foreign:
	Total foreign			8,293,654		3,650,488		4,881		2,021,284		980,343		137		111,684		302,680		15,365,151
	Total			31,480,416		16,484,016		12,583,274		4,899,190		2,578,279		254,119		201,952		1,464,218		69,945,464
	2014
	Domestic:
	Manufacturing			4,248,490		2,467,326		109,258		310,703		636,348		21,117		3,820		228,870		8,025,932
	Construction and real estate			2,890,563		3,066,852		623,385		161,177		303,746		20,577		381		137,913		7,204,594
	Services			1,946,764		1,558,609		205,939		6,998		135,030		24,958		—		78,444		3,956,742
	Wholesale and retail			2,029,723		2,632,048		249,304		63,116		178,520		42,086		10		155,900		5,350,707
	Transportation and communications			2,388,541		658,680		88,911		1,348		50,667		11,159		—		48,088		3,247,394
	Banks and other financial institutions			2,602,545		664,843		2,030		4,780		174,328		165		—		11,456		3,460,147
	Government and public institutions			6,678,104		8,347		—		48,000		—		—		—		—		6,734,451
	Other industries			1,907,714		754,137		3,383		2,240,879		7,804		401		68,642		861		4,983,821
	Individuals			—		197,725		11,266,620		169,655		40,606		101,718		2,823		195,372		11,974,519
	Total domestic			24,692,444		12,008,567		12,548,830		3,006,656		1,527,049		222,181		75,676		856,904		54,938,307
	Foreign:
	Total foreign			10,600,531		4,349,587		6,621		2,782,476		513,610		14		144,238		288,156		18,685,233
	Total			35,292,975		16,358,154		12,555,451		5,789,132		2,040,659		222,195		219,914		1,145,060		73,623,540
	Notes:
	-1	Special attention obligors are watch obligors with debt in TDR or 90 days or more delinquent debt. Loans to such obligors are considered impaired.
	-2	Amounts represent small balance, homogeneous loans which are subject to pool allocations.
	-3	The former MHBK and the former Mizuho Corporate Bank, Ltd. (“MHCB”) merged on July 1, 2013 and the former MHCB, the surviving company, changed its trade name to MHBK. As of March 31, 2013, non-impaired loans held by subsidiaries other than the former MHBK, the former MHCB and MHTB constitute Other, since their portfolio segments are not identical to those used by the former MHBK, the former MHCB and MHTB. As of March 31, 2014, non-impaired loans held by subsidiaries other than MHBK and MHTB constitute Other, since their portfolio segments are not identical to those used by MHBK and MHTB.
Impaired Financing Receivables	'
	The table below presents impaired loans information at March 31, 2013 and 2014.
			Recorded investment (1)						Unpaid		Related		Average		Interest
									principal		allowance (3)		recorded		income
			Requiring an		Not		Total		balance				investment		recognized (4)
			allowance for		requiring an
			loan losses		allowance
					for loan
					losses (2)
			(in millions of yen)
	2013
	Domestic:
	Manufacturing			325,727		10,177		335,904		365,049		118,475		299,978		5,297
	Construction and real estate			189,060		59,973		249,033		269,770		46,574		227,920		2,824
	Services			77,982		12,117		90,099		106,397		22,153		103,113		1,949
	Wholesale and retail			160,477		12,218		172,695		189,231		62,962		186,594		3,076
	Transportation and communications			55,202		3,833		59,035		61,554		18,870		54,633		1,220
	Banks and other financial institutions			13,727		56		13,783		13,821		5,007		11,950		227
	Other industries			5,224		140		5,364		5,484		3,818		4,791		73
	Individuals			116,875		118,750		235,625		252,182		9,429		250,718		4,343
	Total domestic			944,274		217,264		1,161,538		1,263,488		287,288		1,139,697		19,009
	Foreign:
	Total foreign			297,859		4,821		302,680		305,801		119,053		220,561		5,321
	Total			1,242,133		222,085		1,464,218		1,569,289		406,341		1,360,258		24,330
	2014
	Domestic:
	Manufacturing			216,579		12,291		228,870		240,660		74,367		259,889		4,086
	Construction and real estate			107,932		29,981		137,913		163,813		30,724		183,437		2,213
	Services			66,651		11,793		78,444		88,537		20,199		83,754		1,671
	Wholesale and retail			142,886		13,014		155,900		172,641		51,274		161,288		2,795
	Transportation and communications			44,237		3,851		48,088		54,149		14,691		50,387		939
	Banks and other financial institutions			11,390		66		11,456		11,480		4,049		12,474		163
	Other industries			781		80		861		2,020		108		3,486		19
	Individuals			91,715		103,657		195,372		206,341		9,391		215,422		3,714
	Total domestic			682,171		174,733		856,904		939,641		204,803		970,137		15,600
	Foreign:
	Total foreign			276,292		11,864		288,156		290,161		118,360		291,981		4,750
	Total			958,463		186,597		1,145,060		1,229,802		323,163		1,262,118		20,350
	Notes:
	-1	Amounts represent the outstanding balances of nonaccrual loans. The MHFG Group’s policy for placing loans in nonaccrual status completely corresponds to the Group’s definition of impaired loans.
	-2	These impaired loans do not require an allowance for loan losses because the MHFG Group has sufficient collateral to cover probable loan losses.
	-3	The allowance for loan losses on impaired loans includes those for groups of small balance, homogeneous loans totaling ¥504,750 million and ¥425,391 million as of March 31, 2013 and 2014 which were collectively evaluated for impairment, in addition to those that were individually evaluated for impairment.
	-4	Amounts represent gross interest income on impaired loans which were included in Interest income on loans in the consolidated statements of income.
Troubled Debt Restructurings on Financing Receivables Subsequently Defaulted	'
	The following table presents TDRs that were made during the fiscal years ended March 31, 2013 and 2014.
			Loan forgiveness or debt to				Interest rate
			equity swaps				reduction and/or
							Postponement of
							principal and/or
			Recorded		Charge-offs (2)		interest
			investment (1)
					(in millions of yen)
	2013
	Domestic:
	Manufacturing			—		—		277,957
	Construction and real estate			—		—		129,908
	Services			—		—		68,930
	Wholesale and retail			—		1,243		218,497
	Transportation and communications			—		—		52,206
	Banks and other financial institutions			—		—		34,468
	Other industries			—		—		1,809
	Individuals			—		—		62,160
	Total domestic			—		1,243		845,935
	Foreign:
	Total foreign			1,062		3,750		140,064
	Total			1,062		4,993		985,999
	2014
	Domestic:
	Manufacturing			235		481		196,705
	Construction and real estate			2,528		136		44,573
	Services			310		555		57,945
	Wholesale and retail			5		149		170,217
	Transportation and communications			—		—		34,598
	Banks and other financial institutions			—		—		31,901
	Other industries			—		—		1,998
	Individuals			—		—		47,822
	Total domestic			3,078		1,321		585,759
	Foreign:
	Total foreign			—		—		60,348
	Total			3,078		1,321		646,107
	Notes:
	-1	Amounts represent the book values of loans immediately after the restructurings.
	-2	Charge-offs represent the loss impact on the consolidated statements of income for the fiscal year that resulted from the restructurings.
Troubled Debt Restructurings on Financing Receivables by Type of Restructuring	'
	The following table presents payment defaults which occurred during the fiscal years ended March 31, 2013 and 2014 with respect to the loans modified as TDRs within the previous twelve months.
			Recorded investment
			2013		2014
			(in millions of yen)
	Domestic:
	Manufacturing			18,740		21,144
	Construction and real estate			18,751		3,500
	Services			5,976		3,707
	Wholesale and retail			19,920		21,916
	Transportation and communications			4,386		14,069
	Banks and other financial institutions			—		—
	Other industries			—		107
	Individuals			5,517		6,283
	Total domestic			73,290		70,726
	Foreign:
	Total foreign			6,374		115
	Total			79,664		70,841
Financing Receivable, by Contractual Maturity	'
	The table below presents an analysis of the age of the recorded investment in loans that are past due at March 31, 2013 and 2014:
			30-59 days		60-89 days		90 days or		Total past		Current		Total
			past due		past due		more past due		due
			(in millions of yen)
	2013
	Domestic:
	Manufacturing			3,788		1,911		32,830		38,529		8,040,342		8,078,871
	Construction and real estate			11,815		4,038		69,333		85,186		7,392,667		7,477,853
	Services			3,385		1,916		13,829		19,130		3,952,881		3,972,011
	Wholesale and retail			2,771		2,851		16,483		22,105		5,333,869		5,355,974
	Transportation and communications			711		558		3,687		4,956		3,142,150		3,147,106
	Banks and other financial institutions			—		—		6		6		3,142,992		3,142,998
	Government and public institutions			—		—		—		—		6,907,426		6,907,426
	Other industries			—		18		122		140		4,521,854		4,521,994
	Individuals			41,987		24,114		69,774		135,875		11,840,205		11,976,080
	Total domestic			64,457		35,406		206,064		305,927		54,274,386		54,580,313
	Foreign:
	Total foreign			127		885		11,132		12,144		15,353,007		15,365,151
	Total			64,584		36,291		217,196		318,071		69,627,393		69,945,464
	2014
	Domestic:
	Manufacturing			2,834		2,193		14,452		19,479		8,006,453		8,025,932
	Construction and real estate			5,412		3,440		44,852		53,704		7,150,890		7,204,594
	Services			2,185		1,235		10,304		13,724		3,943,018		3,956,742
	Wholesale and retail			3,205		4,561		12,180		19,946		5,330,761		5,350,707
	Transportation and communications			832		573		3,265		4,670		3,242,724		3,247,394
	Banks and other financial institutions			—		1		5		6		3,460,141		3,460,147
	Government and public institutions			—		—		—		—		6,734,451		6,734,451
	Other industries			9		29		34		72		4,983,749		4,983,821
	Individuals			38,466		18,488		56,605		113,559		11,860,960		11,974,519
	Total domestic			52,943		30,520		141,697		225,160		54,713,147		54,938,307
	Foreign:
	Total foreign			87		23		10,935		11,045		18,674,188		18,685,233
	Total			53,030		30,543		152,632		236,205		73,387,335		73,623,540

Allowance_for_loan_losses_Tabl

Allowance for loan losses (Tables)	12 Months Ended
	Mar. 31, 2014
Allowance for Credit Losses on Financing Receivables	'
	Changes in the Allowance for loan losses by portfolio segment for the fiscal years ended March 31, 2012, 2013 and 2014 are shown below:
		Corporate			Retail			Other		Total
		(in millions of yen)
	2012
	Balance at beginning of fiscal year		563,116			151,342			20,072		734,530
	Provision (credit) for loan losses		(19,433	)		(21,375	)		17,764		(23,044	)
	Charge-offs		54,599			5,133			20,410		80,142
	Less: Recoveries		48,354			1,442			2,460		52,256
	Net charge-offs		6,245			3,691			17,950		27,886
	Others (Note)		(1,963	)		—			1,055		(908	)
	Balance at end of fiscal year		535,475			126,276			20,941		682,692
	2013
	Balance at beginning of fiscal year		535,475			126,276			20,941		682,692
	Provision (credit) for loan losses		137,549			(14,180	)		16,578		139,947
	Charge-offs		69,845			4,249			20,503		94,597
	Less: Recoveries		27,447			1,342			2,911		31,700
	Net charge-offs		42,398			2,907			17,592		62,897
	Others (Note)		11,269			—			1,946		13,215
	Balance at end of fiscal year		641,895			109,189			21,873		772,957
	2014
	Balance at beginning of fiscal year		641,895			109,189			21,873		772,957
	Provision (credit) for loan losses		(128,368	)		(12,712	)		14,850		(126,230	)
	Charge-offs		47,927			3,935			13,286		65,148
	Less: Recoveries		21,423			3,000			2,112		26,535
	Net charge-offs		26,504			935			11,174		38,613
	Others (Note)		14,326			—			3,737		18,063
	Balance at end of fiscal year		501,349			95,542			29,286		626,177
	Note: Others include primarily foreign exchange translation.
	The table below presents the Allowance for loan losses and loans outstanding by portfolio segment disaggregated on the basis of impairment method at March 31, 2013 and 2014:
		Corporate			Retail			Other		Total
		(in millions of yen)
	2013
	Allowance for loan losses		641,895			109,189			21,873		772,957
	of which individually evaluated for impairment		398,622			14,815			9,247		422,684
	of which collectively evaluated for impairment		243,273			94,374			12,626		350,273
	Loans (Note)		51,801,814			13,007,792			5,135,858		69,945,464
	of which individually evaluated for impairment		1,160,489			45,961			59,974		1,266,424
	of which collectively evaluated for impairment		50,641,325			12,961,831			5,075,884		68,679,040
	2014
	Allowance for loan losses		501,349			95,542			29,286		626,177
	of which individually evaluated for impairment		327,011			11,735			10,562		349,308
	of which collectively evaluated for impairment		174,338			83,807			18,724		276,869
	Loans (Note)		54,651,867			12,922,564			6,049,109		73,623,540
	of which individually evaluated for impairment		1,100,938			39,250			54,127		1,194,315
	of which collectively evaluated for impairment		53,550,929			12,883,314			5,994,982		72,429,225
	Note: Amounts represent loan balances before deducting unearned income and deferred loan fees.

Premises_and_equipment_Tables

Premises and equipment (Tables)	12 Months Ended
	Mar. 31, 2014
Property, Plant and Equipment	'
	Premises and equipment at March 31, 2013 and 2014 consist of the following:
		2013		2014
		(in millions of yen)
	Land		268,948		410,739
	Buildings		743,473		800,680
	Equipment and furniture		418,647		435,655
	Leasehold improvements		90,306		92,052
	Construction in progress		23,875		35,789
	Software		657,702		725,287
	Total		2,202,951		2,500,202
	Less: Accumulated depreciation and amortization		1,110,962		1,143,608
	Premises and equipment—net		1,091,989		1,356,594

Goodwill_and_intangible_assets1

Goodwill and intangible assets (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Goodwill	'
	The changes in Goodwill during the fiscal years ended March 31, 2012, 2013 and 2014 were as follows:
			MHBK			Total
			(in millions of yen)
	2012
	Balance at beginning of fiscal year			7,610			7,610
	Goodwill acquired (1)			3,776			3,776
	Impairment losses recognized			5,637			5,637
	Foreign exchange translation			(114	)		(114	)
	Balance at end of fiscal year			5,635			5,635
	Gross amount of goodwill			70,909			70,909
	Accumulated impairment losses			65,274			65,274
	2013
	Balance at beginning of fiscal year			5,635			5,635
	Goodwill acquired			—			—
	Impairment losses recognized			—			—
	Foreign exchange translation			512			512
	Balance at end of fiscal year			6,147			6,147
	Gross amount of goodwill			71,421			71,421
	Accumulated impairment losses			65,274			65,274
	2014
	Balance at beginning of fiscal year			6,147			6,147
	Goodwill acquired (2)			7,719			7,719
	Impairment losses recognized			3,792			3,792
	Foreign exchange translation			1,475			1,475
	Balance at end of fiscal year			11,549			11,549
	Gross amount of goodwill			80,615			80,615
	Accumulated impairment losses			69,066			69,066
	Notes:
	-1	Goodwill acquired is entirely related to the acquisition of PT. Mizuho Balimor Finance.
	-2	Goodwill acquired is entirely related to the acquisition of Banco Mizuho do Brasil S.A.
Schedule of Intangible Assets by Major Class	'
	The table below presents the gross carrying amount, accumulated amortization and net carrying amount of intangible assets, at March 31, 2013 and 2014.
			2013								2014
			Gross			Accumulated			Net		Gross		Accumulated		Net
			carrying			amortization			carrying		carrying		amortization		carrying
			amount						amount		amount				amount
			(in millions of yen)
	Intangible assets subject to amortization:
	Customer relationships (Note)			73,949			19,238			54,711		73,949		24,865		49,084
	Other			2,363			2,050			313		2,808		2,152		656
	Total			76,312			21,288			55,024		76,757		27,017		49,740
	Intangible assets not subject to amortization:
	Total			9,450			—			9,450		9,207		—		9,207
	Total			85,762			21,288			64,474		85,964		27,017		58,947
	Note:	Customer relationships were acquired by the merger of MHSC and Shinko on May 7, 2009. See Note 1 “Basis of presentation and summary of significant accounting policies” for further information.
Schedule of Expected Amortization Expense	'
	The table below presents the estimated aggregate amortization expenses for intangible assets for the next five years:
			(in millions of yen)
	Fiscal year ending March 31:
	2015			5,349
	2016			5,058
	2017			4,780
	2018			4,502
	2019			4,264

Pledged_assets_and_collateral_

Pledged assets and collateral (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Assets Pledged as Collateral	'
	The following amounts, by balance sheet classification, have been pledged as collateral for borrowings and for other purposes at March 31, 2013 and 2014:
		2013		2014
		(in billions of yen)
	Interest-bearing deposits in other banks		28		38
	Trading account assets		13,752		10,271
	Available-for-sale securities		15,939		13,353
	Loans		8,860		8,796
	Other assets		900		677
	Total		39,479		33,135
Schedule of Secured Borrowings	'
	The associated liabilities collateralized by the above assets at March 31, 2013 and 2014 are summarized below:
		2013		2014
		(in billions of yen)
	Deposits		259		878
	Call money and funds purchased		1,580		1,708
	Payables under repurchase agreements		7,726		6,884
	Payables under securities lending transactions		11,092		6,237
	Other short-term borrowings		5,626		405
	Long-term debt		321		5,632
	Total		26,604		21,744

Deposits_Tables

Deposits (Tables)	12 Months Ended
	Mar. 31, 2014
Deposit Liabilities Table Disclosures	'
	The balances of time deposits and certificates of deposit issued by domestic offices in amounts of ¥10 million (approximately US$97 thousand at the Federal Reserve Bank of New York’s noon buying rate on March 31, 2014) or more and the balances of those deposits issued by foreign offices in amounts of US$100,000 or more at March 31, 2013 and 2014 are as follows:
		2013		2014
		(in millions of yen)
	Domestic offices:
	Time deposits		18,302,196		18,351,826
	Certificates of deposit		11,393,094		8,117,512
	Total		29,695,290		26,469,338
	Foreign offices:
	Time deposits		8,209,016		9,555,568
	Certificates of deposit		3,933,688		4,638,265
	Total		12,142,704		14,193,833
Interest Bearing Deposit Liabilities by Maturity Disclosures	'
	The balance and remaining maturities of time deposits and certificates of deposit issued by domestic and foreign offices at March 31, 2014 are shown in the following table:
		Time		Certificates of		Total
		deposits		deposit
		(in millions of yen)
	Domestic offices:
	Due in one year or less		24,079,640		8,115,532		32,195,172
	Due after one year through two years		1,910,790		1,980		1,912,770
	Due after two years through three years		1,243,980		—		1,243,980
	Due after three years through four years		342,948		—		342,948
	Due after four years through five years		412,261		—		412,261
	Due after five years		133,735		—		133,735
	Total		28,123,354		8,117,512		36,240,866
	Foreign offices:
	Due in one year or less		9,526,641		4,630,546		14,157,187
	Due after one year through two years		20,176		7,719		27,895
	Due after two years through three years		9,528		—		9,528
	Due after three years through four years		1,102		—		1,102
	Due after four years through five years		3,240		—		3,240
	Due after five years		392		—		392
	Total		9,561,079		4,638,265		14,199,344
	Total		37,684,433		12,755,777		50,440,210

Shortterm_borrowings_and_longt1

Short-term borrowings and long-term debt (Tables)	12 Months Ended
	Mar. 31, 2014
Details of Other Short-Term Borrowings	'
	Details of Other short-term borrowings at March 31, 2013 and 2014 are as follows:
			2013		2014
			(in millions of yen)
	Commercial paper and short-term notes issued by consolidated VIEs of asset-backed commercial paper programs (1) (2)			252,277		286,968
	Short-term notes issued by MHFG and its subsidiaries (1)			477,400		497,100
	Borrowings from the Bank of Japan			5,884,304		5,138,003
	Other			110,119		101,901
	Total			6,724,100		6,023,972
	Notes:
	-1	Short-term notes are issued under laws of Japan in the form of dematerialized commercial paper, whose characteristics are economically the same as commercial paper.
	-2	Commercial paper and short-term notes issued by consolidated VIEs of asset-backed commercial paper programs in the above table consist of commercial paper and short-term notes, of which amounts were ¥164,194 million and ¥88,083 million, respectively, at March 31, 2013, and ¥199,500 million and ¥87,468 million, respectively, at March 31, 2014.
Long-Term Obligations	'
	Long-term debt with original maturities of more than one year at March 31, 2013 and 2014 is comprised of the following:
			2013		2014
			(in millions of yen)
	Obligations under capital leases			24,406		26,680
	Loan participation borrowings			62,332		79,014
	Senior borrowings and bonds			4,784,010		5,805,634
	Subordinated borrowings and bonds			3,931,475		3,942,613
	Total			8,802,223		9,853,941
Schedule of Long-term Debt Instruments	'
	The following table presents the interest rates and maturities of senior borrowings and bonds, and subordinated borrowings and bonds:
			Interest rates (1)		Maturities (2)		2013		2014
			(%)				(in millions of yen)
	Senior borrowings and bonds:
	fixed rate denominated in Japanese yen			0.00-10.00		Apr. 2014-Mar. 2044		2,741,475		3,557,508
	fixed rate denominated in U.S. dollars			0.00-7.49		Apr. 2014-Jul. 2043		520,714		604,281
	fixed rate denominated in other currencies			0.02-5.40		Jan. 2015-Mar. 2029		683		25,687
	floating rate denominated in Japanese yen			0.00-18.10		Apr. 2014-Mar. 2044		1,065,708		1,063,111
	floating rate denominated in U.S. dollars			0.00-15.60		Apr. 2014-Mar. 2028		426,515		532,199
	floating rate denominated in other currencies			0.05-0.58		Apr. 2014-Jan. 2015		28,915		22,848
	Total							4,784,010		5,805,634
	Subordinated borrowings and bonds:
	fixed rate denominated in Japanese yen			1.09-4.74		Apr. 2014-Perpetual		3,393,092		3,249,999
	fixed rate denominated in U.S. dollars			4.30-14.91		Apr. 2014-Perpetual		419,383		613,609
	floating rate denominated in Japanese yen			0.98-2.61		Jun. 2019-Perpetual		119,000		79,005
	Total							3,931,475		3,942,613
	Total							8,715,485		9,748,247
	Notes:
	-1	The interest rates disclosed reflect the range of contractual rates in effect at March 31, 2014.
	-2	Maturity information disclosed is the range of maturities at March 31, 2014.
	-3	None of the long-term debt issuances above are convertible to common stock.
	-4	Certain debt agreements permit the MHFG Group to redeem the related debt, in whole or in part, prior to maturity at the MHFG Group’s option on terms specified in the respective agreements.
Schedule of Maturities of Long-term Debt	'
	The following is a summary of the contractual maturities of long-term debt subsequent to March 31, 2014:
			(in millions of yen)
	Fiscal year ending March 31:
	2015			1,222,317
	2016			1,190,985
	2017			1,776,546
	2018			1,025,441
	2019			483,888
	2020 and thereafter			4,154,764
	Total			9,853,941

Other_assets_and_liabilities_T

Other assets and liabilities (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Other Assets and Other Liabilities	'
	The following table sets forth the details of other assets and liabilities at March 31, 2013 and 2014:
		2013		2014
		(in millions of yen)
	Other assets:
	Accounts receivable from brokers, dealers and customers for securities transactions		907,671		1,122,247
	Collateral provided for derivative transactions		742,307		466,420
	Prepaid pension cost		153,414		403,654
	Miscellaneous receivables		120,322		315,037
	Margins provided for futures contracts		99,844		147,376
	Security deposits		102,031		121,675
	Loans held for sale		9,820		58,745
	Other		466,542		563,841
	Total		2,601,951		3,198,995
	Other liabilities:
	Accounts payable to brokers, dealers and customers for securities transactions		1,560,345		1,325,455
	Guaranteed trust principal		535,720		591,647
	Miscellaneous payables		260,665		473,028
	Collateral accepted for derivative transactions		503,101		432,820
	Factoring amounts owed to customers		375,933		382,189
	Margins accepted for futures contracts		199,930		289,381
	Unearned income		141,189		141,735
	Other		791,243		785,768
	Total		4,368,126		4,422,023

Preferred_stock_Tables

Preferred stock (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Conversions of Stock	'
	Each share of preferred stock which has not been converted as described above by the end of the relevant conversion period will be converted into common stock on the day following the end of the conversion period on the following terms:
			Conversion date		Conversion ratio
	Eleventh series class XI preferred stock		1-Jul-16		¥1,000/(current market price), where the current market price is the average price of daily closing prices (including closing bid or offered price) of common stock as reported by the TSE for the 30 consecutive trading days (excluding trading days on which no closing price, closing bid or offered price is reported) commencing on the 45th trading day prior to July 1, 2016, provided that the current market price shall not be less than ¥282.90.
Schedule of Stockholders Equity	'
	The changes in the number of shares and the aggregate amount of preferred stock during the fiscal years ended March 31, 2012, 2013 and 2014 were as follows:
	Class of stock		Issued at			Net		Issued at		Net		Issued at		Net			Issued at
			March 31,			change		March 31,		change		March 31,		change			March 31,
			2011					2012				2013					2014
			(number of shares)
	Eleventh series class XI preferred stock (Note)			914,752,000			—		914,752,000		—		914,752,000		—			914,752,000
	Thirteenth series class XIII preferred stock			36,690,000			—		36,690,000		—		36,690,000		(36,690,000	)		—
	Total			951,442,000			—		951,442,000		—		951,442,000		(36,690,000	)		914,752,000
	Class of stock		Aggregate			Net		Aggregate		Net		Aggregate		Net			Aggregate
			amount at			change		amount at		change		amount at		change			amount at
			March 31,					March 31,				March 31,					March 31,
			2011					2012				2013					2014
			(in millions of yen)
	Eleventh series class XI preferred stock (Note)			914,752			—		914,752		—		914,752		—			914,752
	Thirteenth series class XIII preferred stock			36,690			—		36,690		—		36,690		(36,690	)		—
	Total			951,442			—		951,442		—		951,442		(36,690	)		914,752
	Note:	The aggregate amount and number of issued shares include the preferred stock in treasury which has been converted to common stock but not yet cancelled.
Preferred stock	'
Schedule of Stock by Class	'
	The composition of preferred stock at March 31, 2012, 2013 and 2014 is as follows:
	2012		Aggregate amount			Number of shares						Liquidation		Convertible
	Class of stock					Authorized		Issued		In treasury		value per share		or not
			(in millions of yen)									(in yen)
	Eleventh series class XI preferred stock (1)			914,752			1,369,512,000		914,752,000		541,073,800		1,000		Yes
	Class XII preferred stock			—			1,500,000,000		—		—		—		—
	Thirteenth series class XIII preferred stock			36,690			1,500,000,000		36,690,000		—		1,000		No
	Total			951,442			4,369,512,000		951,442,000		541,073,800
	2013		Aggregate amount			Number of shares						Liquidation		Convertible
	Class of stock					Authorized		Issued		In treasury		value per share		or not
			(in millions of yen)									(in yen)
	Eleventh series class XI preferred stock (1)			914,752			1,369,512,000		914,752,000		574,087,800		1,000		Yes
	Class XII preferred stock			—			1,500,000,000		—		—		—		—
	Thirteenth series class XIII preferred stock			36,690			1,500,000,000		36,690,000		—		1,000		No
	Total			951,442			4,369,512,000		951,442,000		574,087,800
	2014		Aggregate amount			Number of shares						Liquidation		Convertible
	Class of stock					Authorized		Issued		In treasury		value per share		or not
			(in millions of yen)									(in yen)
	Eleventh series class XI preferred stock (1)			914,752			914,752,000		914,752,000		602,100,700		1,000		Yes
	Thirteenth series class XIII preferred stock			—			36,690,000		—		—		—		—
	First series class XIV preferred stock (2)			—			900,000,000		—		—		—		—
	Second series class XIV preferred stock (2)			—			900,000,000		—		—		—		—
	Third series class XIV preferred stock (2)			—			900,000,000		—		—		—		—
	Fourth series class XIV preferred stock (2)			—			900,000,000		—		—		—		—
	First series class XV preferred stock (3)			—			900,000,000		—		—		—		—
	Second series class XV preferred stock (3)			—			900,000,000		—		—		—		—
	Third series class XV preferred stock (3)			—			900,000,000		—		—		—		—
	Fourth series class XV preferred stock (3)			—			900,000,000		—		—		—		—
	First series class XVI preferred stock (4)			—			1,500,000,000		—		—		—		—
	Second series class XVI preferred stock (4)			—			1,500,000,000		—		—		—		—
	Third series class XVI preferred stock (4)			—			1,500,000,000		—		—		—		—
	Fourth series class XVI preferred stock (4)			—			1,500,000,000		—		—		—		—
	Total			914,752			4,251,442,000		914,752,000		602,100,700
	Notes:
	-1	The aggregate amount and number of issued shares include the preferred stock in treasury which has been converted to common stock but not yet cancelled.
	-2	The total number of authorized shares from first to fourth series class XIV preferred stock shall not exceed 900,000,000.
	-3	The total number of authorized shares from first to fourth series class XV preferred stock shall not exceed 900,000,000.
	-4	The total number of authorized shares from first to fourth series class XVI preferred stock shall not exceed 1,500,000,000.
Convertible Preferred Stock	'
Schedule of Stock by Class	'
	Eleventh series class XI preferred stock is convertible into common stock at the option of the holder. The material terms and conditions of conversion are as follows.
			Conversion period		Conversion ratio (Note)
	Eleventh series class XI preferred stock		July 1, 2008 to		¥1,000/(conversion price), where the conversion price after adjustment is ¥282.90 on or after August 30, 2011; to be reset on July 1, 2014 and 2015 (each, a “Reset Date”) as ¥1,000/(conversion price), where the conversion price is the lower of (x) the average price of daily closing prices (including closing bid or offered price) of common stock as reported by the Tokyo Stock Exchange (“TSE”) for the 30 consecutive trading days (excluding trading days on which no closing price, closing bid or offered price is reported) commencing on the 45th trading day prior to the Reset Date and (y) the conversion price after adjustment effective as of the day before the relevant Reset Date, provided that the conversion price shall not be less than ¥282.90.
			30-Jun-16
	Note:	Subject to adjustment, where issuance or disposal by MHFG of common stock for a price below the “current market price”, a stock split, issuance of securities convertible into common stock at a price below the “current market price” at the time of issuance thereof or determination of the conversion price thereof, merger or amalgamation, or a capital decrease or stock consolidation occurs and in certain other circumstances.
Common Stock	'
Schedule of Stock by Class	'
	The changes in the number of issued shares of common stock during the fiscal years ended March 31, 2012, 2013 and 2014 were as follows:
			2012			2013		2014
			(shares)
	Balance at beginning of fiscal year			21,782,185,320			24,048,165,727		24,164,864,477
	Issuance of new shares of common stock by conversion of Eleventh series class XI preferred stock			151,921,540			116,698,750		99,020,710
	Issuance of new shares of common stock by exercise of stock acquisition rights			4,748,000			—		—
	Issuance of new shares of common stock for stock exchanges			2,109,310,867			—		—
	Balance at end of fiscal year			24,048,165,727			24,164,864,477		24,263,885,187

Dividends_Tables

Dividends (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Dividends Payable	'
	Dividends on preferred stock and common stock during the fiscal years ended March 31, 2012, 2013 and 2014 were as follows:
	2012		Cash dividends (1)
	Class of stock		Per share		In aggregate (2)
			(in yen)		(in millions of yen)
	Eleventh series class XI preferred stock			30		12,173
	Thirteenth series class XIII preferred stock			45		1,651
	Common stock			9		202,684
	Total					216,508
	2013		Cash dividends
	Class of stock		Per share		In aggregate (2)
			(in yen)		(in millions of yen)
	Eleventh series class XI preferred stock			20		7,451
	Thirteenth series class XIII preferred stock			30		1,101
	Common stock			6		144,170
	Total					152,722
	2014		Cash dividends
	Class of stock		Per share		In aggregate (2)
			(in yen)		(in millions of yen)
	Eleventh series class XI preferred stock			20		6,717
	Thirteenth series class XIII preferred stock (3)			15		550
	Common stock			6		144,998
	Total					152,265
	Notes:
	-1	As MHFG commenced distributing an interim dividend from the fiscal year ended March 31, 2012, the amounts for the fiscal year include such interim dividends.
	-2	Dividends paid on treasury stock are excluded.
	-3	On July 11, 2013, MHFG acquired and cancelled all of the shares of the thirteenth series class XIII preferred stock. Consequently, the amount for the fiscal year does not include interim dividends.

Accumulated_other_comprehensiv1

Accumulated other comprehensive income (loss) (Tables)	12 Months Ended
	Mar. 31, 2014
Changes in Each Component of Accumulated Other Comprehensive Income (Loss), Net Of Tax	'
	Changes in each component of AOCI for the fiscal years ended March 31, 2012, 2013 and 2014 are as follows:
			2012			2013			2014
			(in millions of yen)
	AOCI, balance at beginning of fiscal year			104,972			245,588			777,997
	Unrealized net gains (losses) on available-for-sale securities:
	Balance at beginning of fiscal year			514,128			628,636			995,124
	Unrealized holding gains (losses) during year			87,215			427,913			255,140
	Less: reclassification adjustments for losses (gains) included in net income			27,293			(61,425	)		(126,992	)
	Change during year			114,508			366,488			128,148
	Balance at end of fiscal year			628,636			995,124			1,123,272
	Foreign currency translation adjustments:
	Balance at beginning of fiscal year			(165,028	)		(169,881	)		(82,420	)
	Foreign currency translation adjustments during year			(6,779	)		87,460			75,986
	Less: reclassification adjustments for losses (gains) included in net income			1,926			1			—
	Change during year			(4,853	)		87,461			75,986
	Balance at end of fiscal year			(169,881	)		(82,420	)		(6,434	)
	Pension liability adjustments:
	Balance at beginning of fiscal year			(244,128	)		(213,167	)		(134,707	)
	Unrealized gains (losses) during year			14,711			67,795			131,360
	Less: reclassification adjustments for losses (gains) included in net income			16,250			10,665			4,386
	Change during year			30,961			78,460			135,746
	Balance at end of fiscal year			(213,167	)		(134,707	)		1,039
	Total other comprehensive income (loss), net of tax attributable to MHFG shareholders			140,616			532,409			339,880
	AOCI, balance at end of fiscal year			245,588			777,997			1,117,877
Amounts Reclassified Out of Accumulated Other Comprehensive Income (Loss) into Net Income	'
	The following table shows the amounts reclassified out of AOCI into net income during the fiscal year ended March 31, 2014.
			Before			Tax			Net of tax			Net of tax			Net of tax
			tax (1)			effect (2)			before			attributable to			attributable to
									allocation to			noncontrolling			MHFG
									noncontrolling			interests (2)			shareholders
									interests
			(in millions of yen)
	Amounts reclassified out of AOCI into net income:																	Affected line items in the consolidated statements of income:
	Unrealized net gains (losses) on available-for-sale securities			197,224			(70,228	)		126,996			4			126,992		Investment gains (losses)—net
	Foreign currency translation adjustments			—			—			—			—			—
	Pension liability adjustments			(6,877	)		2,442			(4,435	)		(49	)		(4,386	)	Salaries and employee benefits
	Total			190,347			(67,786	)		122,561			(45	)		122,606
	Notes:
	-1	The amounts in the Before tax column are recorded in each account presented as “Affected line items in the consolidated statements of income”.
	-2	The amounts in the Tax effect column and Net of tax attributable to noncontrolling interests column are recorded in Income tax expense and Net income attributable to noncontrolling interests in the consolidated statements of income respectively.

Regulatory_matters_Tables

Regulatory matters (Tables)	12 Months Ended
	Mar. 31, 2014
Capital Requirements and Regulatory Adjustments Over Transitional Period	'
	The capital requirements and regulatory adjustments will be phased in over a transitional period as follows (italicized percentages indicate those still in transition periods):
			March			March			March			March			March			March			March			March			March			March
			2013			2014			2015			2016			2017			2018			2019			2020			2021			2022
	Minimum Common Equity Tier 1 capital (Note)			3.5	%		4	%		4.5	%		4.5	%		4.5	%		4.5	%		4.5	%		4.5	%		4.5	%		4.5	%
	Minimum Tier 1 capital (Note)			4.5	%		5.5	%		6	%		6	%		6	%		6	%		6	%		6	%		6	%		6	%
	Minimum total capital (Note)			8	%		8	%		8	%		8	%		8	%		8	%		8	%		8	%		8	%		8	%
	Capital conservation buffer			0	%		0	%		0	%		0.625	%		1.25	%		1.875	%		2.5	%		2.5	%		2.5	%		2.5	%
	Phase out of recognition of capital instruments that no longer qualify as capital (Note)			90	%		80	%		70	%		60	%		50	%		40	%		30	%		20	%		10	%		0	%
	Phase-in of deductions from capital (Note)			0	%		20	%		40	%		60	%		80	%		100	%		100	%		100	%		100	%		100	%
	Additional loss absorbency requirements for G-SIBs			—			—			—			Additional loss absorption capacity tailored to the
													impact of the entity’s default, ranging from 1% to
													2.5% of risk-weighted assets, to be met with
													Common Equity Tier 1 capital
	Note:	While these measures are included in the revisions to capital adequacy guidelines that have been applied from March 31, 2013 as published by the Financial Services Agency, capital adequacy guidelines related to other requirements under the Basel III rules, such as the capital conservation buffer, countercyclical buffer and additional loss absorbency requirements for G-SIBs/G-SIFIs, have not yet been published.
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations	'
	Capital adequacy ratios of MHFG, MHBK, and MHTB as of March 31, 2013 and 2014 calculated in accordance with Japanese GAAP and guidelines established by the Financial Services Agency are set forth in the following table:
			2013						2014
			Amount			Ratio			Amount			Ratio
			(in billions of yen, except percentages)
	Consolidated:
	MHFG:
	Common Equity Tier 1 capital:
	Required			2,059			3.5			2,411			4
	Actual			4,804			8.16			5,304			8.79
	Tier 1 capital:
	Required			2,647			4.5			3,316			5.5
	Actual			6,487			11.02			6,845			11.35
	Total risk-based capital:
	Required			4,706			8			4,823			8
	Actual			8,345			14.18			8,656			14.35
	MHBK (Note):
	Common Equity Tier 1 capital:
	Required			—			—			2,130			4
	Actual			—			—			5,387			10.11
	Tier 1 capital:
	Required			—			—			2,928			5.5
	Actual			—			—			6,525			12.25
	Total risk-based capital:
	Required			—			—			4,259			8
	Actual			—			—			8,180			15.36
	MHTB:
	Common Equity Tier 1 capital:
	Required			91			3.5			103			4
	Actual			344			13.24			379			14.76
	Tier 1 capital:
	Required			117			4.5			141			5.5
	Actual			344			13.24			379			14.76
	Total risk-based capital:
	Required			208			8			205			8
	Actual			448			17.21			457			17.8
	Non-consolidated:
	MHBK (Note):
	Common Equity Tier 1 capital:
	Required			—			—			2,072			4
	Actual			—			—			5,260			10.15
	Tier 1 capital:
	Required			—			—			2,849			5.5
	Actual			—			—			6,370			12.29
	Total risk-based capital:
	Required			—			—			4,144			8
	Actual			—			—			8,072			15.58
	MHTB:
	Common Equity Tier 1 capital:
	Required			90			3.5			101			4
	Actual			345			13.45			375			14.76
	Tier 1 capital:
	Required			115			4.5			139			5.5
	Actual			345			13.45			375			14.76
	Total risk-based capital:
	Required			205			8			203			8
	Actual			446			17.43			451			17.79
	Note:	The former MHBK and the former MHCB merged on July 1, 2013 and the former MHCB, the surviving company, changed its trade name to MHBK.
	Capital adequacy ratios of the former MHCB and the former MHBK as of March 31, 2013 are set forth in the following table:
			March 31, 2013
			Consolidated						Non-consolidated
			Amount			Ratio			Amount			Ratio
			(in billions of yen, except percentages)
	The former MHCB (1):
Common Equity Tier 1 capital:
Required			1,292			3.5			1,143			3.5
Actual			3,195			8.65			2,993			9.16
Tier 1 capital:
Required			1,661			4.5			1,470			4.5
Actual			4,071			11.03			3,980			12.18
Total risk-based capital:
Required			2,953			8			2,613			8
Actual			5,130			13.89			5,008			15.33
The former MHBK (2) (3):
Common Equity Tier 1 capital:
Required			810			3.5			793			3.5
Actual			2,061			8.9			2,009			8.86
Tier 1 capital:
Required			1,041			4.5			1,020			4.5
Actual			2,344			10.13			2,252			9.93
Total risk-based capital:
Required			1,850			8			1,813			8
Actual			3,259			14.08			3,163			13.95
Notes:
-1	The distribution of all of the shares of MHSC to MHFG as a dividend in kind (¥424.4 billion) on April 1, 2013 was deducted from Common Equity Tier 1 capital.
-2	The amounts and ratios were calculated in accordance with Basel III and are included for reference purpose only because the former MHBK was subject to Basel II requirements as of March 31, 2013 as a financial institution without overseas operations to which only domestic capital adequacy requirements applied.
-3	The distribution of all of the shares of MHSC to MHFG as a dividend in kind (¥125.7 billion) on April 1, 2013 was deducted from Common Equity Tier 1 capital.

Earnings_per_common_share_Tabl

Earnings per common share (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Calculation of Numerator and Denominator in Earnings Per Share	'
	The following table sets forth the computation of basic and diluted earnings per common share for the fiscal years ended March 31, 2012, 2013 and 2014:
			2012		2013		2014
			(in millions of yen)
	Net income:
	Net income attributable to MHFG shareholders			656,389		875,412		498,484
	Less: Net income attributable to preferred shareholders			8,672		8,221		6,745
	Net income attributable to common shareholders			647,717		867,191		491,739
	Effect of dilutive securities:
	Convertible preferred stock			7,571		7,121		6,437
	Net income attributable to common shareholders after assumed conversions			655,288		874,312		498,176
			2012		2013		2014
			(thousands of shares)
	Shares:
	Weighted average common shares outstanding			23,073,544		24,053,282		24,189,670
	Effect of dilutive securities:
	Convertible preferred stock (Note)			1,384,367		1,291,854		1,164,941
	Stock compensation-type stock options			11,628		20,093		16,641
	Weighted average common shares after assumed conversions			24,469,539		25,365,229		25,371,252
			2012		2013		2014
			(in yen)
	Amounts per common share:
	Basic net income per common share			28.07		36.05		20.33
	Diluted net income per common share			26.78		34.47		19.64
	Note:	The number of the dilutive common shares is based on the applicable conversion prices.

Income_taxes_Tables

Income taxes (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Components of Income Tax Expense (Benefit)	'
	The following table presents the components of Income tax expense for the fiscal years ended March 31, 2012, 2013 and 2014:
			2012			2013			2014
			(in millions of yen)
	Current:
	Domestic			22,103			37,101			92,814
	Foreign			32,714			10,754			42,919
	Total current tax expense			54,817			47,855			135,733
	Deferred:
	Domestic			(36,777	)		(40,021	)		94,911
	Foreign			(4,162	)		(3,810	)		(4,536	)
	Total deferred tax expense			(40,939	)		(43,831	)		90,375
	Total income tax expense			13,878			4,024			226,108
Comprehensive Income Tax (Expense) Benefit Components	'
	The detailed amounts recorded directly in Equity are as follows:
			2012			2013			2014
			(in millions of yen)
	Unrealized net gains (losses) on available-for-sale securities:
	Unrealized gains (losses)			29,925			235,274			161,269
	Less: reclassification adjustments			18,249			(33,988	)		(70,228	)
	Total			48,174			201,286			91,041
	Pension liability adjustments:
	Unrealized gains (losses)			2,367			34,171			71,646
	Less: reclassification adjustments			8,992			5,913			2,442
	Total			11,359			40,084			74,088
	Total tax effect before allocation to noncontrolling interests			59,533			241,370			165,129
Schedule of Effective Income Tax Rate Reconciliation	'
	The following table shows a reconciliation of Income tax expense at the effective statutory tax rate to the actual income tax expense for the fiscal years ended March 31, 2012, 2013 and 2014:
			2012			2013			2014
			(in millions of yen, except tax rates)
	Income before income tax expense (benefit)			662,835			885,180			726,343
	Effective statutory tax rate			40.69	%		38.01	%		38.01	%
	Income tax calculated at the statutory tax rate			269,708			336,457			276,083
	Income not subject to tax			(18,295	)		(18,320	)		(22,354	)
	Expenses not deductible for tax purposes			1,469			1,348			1,550
	Tax rate differentials of subsidiaries			(4,142	)		(10,535	)		(1,611	)
	Change in valuation allowance			(371,271	)		(1,352,597	)		(50,933	)
	Change in undistributed earnings of subsidiaries			(7,118	)		12,233			932
	Change in net operating loss carryforwards resulting from intercompany capital transactions			162			227			235
	Expiration of net operating loss carryforwards			33,576			1,026,439			6,313
	Effect of enacted change in tax rates			107,011	(1)		—			15,786	(2)
	Other			2,778			8,772			107
	Income tax expense (benefit)			13,878			4,024			226,108
	Notes:
	-1	On November 30, 2011, the National Diet of Japan approved two bills affecting the statutory tax rates of MHFG and its domestic subsidiaries. As a result, the statutory tax rate concerning MHFG’s tax returns for the fiscal years ended March 31, 2013 and 2014 has been reduced to 38.01% from the previous rate of 40.69%. Also, the rates for the fiscal year ending March 31, 2015 and for the fiscal years ending March 31, 2016 and thereafter will be 38.01% and 35.64%, respectively. The decrease of the Group’s balance of net deferred tax assets, reflecting such tax rate reductions, was recognized in Income tax expense in the fiscal year ended March 31, 2012.
	-2	On March 20, 2014, the National Diet of Japan approved a bill affecting the statutory tax rates of MHFG and its domestic subsidiaries. As a result, the statutory tax rate concerning MHFG’s tax returns for the fiscal year ending March 31, 2015 will be reduced to 35.64% from the previous rate of 38.01%. The decrease of the Group’s balance of net deferred tax assets, reflecting such tax rate reductions, was recognized in Income tax expense in the fiscal year ended March 31, 2014.
Schedule of Deferred Tax Assets and Liabilities	'
	The components of net deferred tax assets at March 31, 2013 and 2014 are as follows:
			2013			2014
			(in millions of yen)
	Deferred tax assets:
	Investments			889,305			724,038
	Allowance for loan losses			337,453			266,595
	Derivative financial instruments			—			29,002
	Trading account assets			—			19,842
	Net operating loss carryforwards			450,016			448,926
	Other			264,661			204,304
				1,941,435			1,692,707
	Valuation allowance			(584,665	)		(443,847	)
	Deferred tax assets, net of valuation allowance			1,356,770			1,248,860
	Deferred tax liabilities:
	Available-for-sale securities			567,608			659,448
	Prepaid pension cost and accrued pension liabilities			39,937			132,738
	Undistributed earnings of subsidiaries			11,040			11,972
	Premises and equipment			12,304			11,263
	Derivative financial instruments			35,391			—
	Trading account assets			11,101			—
	Other			51,913			61,500
	Deferred tax liabilities			729,294			876,921
	Net deferred tax assets			627,476			371,939
Summary of Operating Loss Carryforwards	'
	These carryforwards are scheduled to expire as follows:
			Net operating loss
			carryforwards
			(in billions of yen)
	Fiscal year ending March 31:
	2015			—
	2016			—
	2017			—
	2018			865
	2019			8
	2020 and thereafter			541
	Total			1,414
Reconciliation Of Unrecognized Tax Benefits	'
	The following table is a roll-forward of unrecognized tax benefits for the fiscal years ended March 31, 2012, 2013 and 2014:
			2012			2013			2014
			(in millions of yen)
	Total unrecognized tax benefits at beginning of fiscal year			1,829			2,160			1,454
	Gross amount of increases (decreases) related to positions taken during prior years			362			(471	)		(6	)
	Gross amount of increases related to positions taken during the current year			244			29			100
	Amount of decreases related to settlements			(227	)		(559	)		—
	Foreign exchange translation			(48	)		295			143
	Total unrecognized tax benefits at end of fiscal year			2,160			1,454			1,691

Pension_and_other_employee_ben1

Pension and other employee benefit plans (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Net Benefit Costs	'
	Net periodic benefit cost of the severance indemnities and pension plans for the fiscal years ended March 31, 2012, 2013 and 2014 includes the following components:
			2012			2013			2014
			(in millions of yen)
	Service cost-benefits earned during the fiscal year			27,734			30,422			33,429
	Interest costs on projected benefit obligation			24,267			23,186			20,341
	Expected return on plan assets			(28,234	)		(32,237	)		(37,047	)
	Amortization of prior service benefit			(318	)		(319	)		(195	)
	Amortization of net actuarial loss (gain)			25,595			16,936			7,039
	Special termination benefits (Note)			14,115			5,454			5,429
	Net periodic benefit cost			63,159			43,442			28,996
	Note:	The amount for the fiscal year ended March 31, 2012 includes special termination benefits of ¥9,828 million pertaining to MHSC’s voluntary retirement scheme.
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	'
	Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss) before-tax for the fiscal years ended March 31, 2013 and 2014 were summarized as follows:
			2013			2014
			(in millions of yen)
	Net actuarial gain (loss)			103,683			204,506
	Amortization of net actuarial loss (gain)			16,936			7,039
	Prior service benefit (cost)			(1,782	)		—
	Amortization of prior service benefit			(319	)		(195	)
	Total recognized in other comprehensive income (loss) before-tax			118,518			211,350
Schedule of Assumptions Used	'
	Weighted-average assumptions used to determine benefit obligations and net periodic benefit cost are as follows:
			2012			2013			2014
	Weighted-average assumptions used to determine benefit obligations at fiscal year end:
	Discount rates			1.73	%		1.44	%		0.96	%
	Rates of increase in future compensation levels			2.33-6.46	%		2.31-6.57	%		2.00-4.80	%
	Weighted-average assumptions used to determine net periodic benefit cost during the year:
	Discount rates			1.83	%		1.73	%		1.44	%
	Rates of increase in future compensation levels			2.28-6.15	%		2.33-6.46	%		2.31-6.57	%
	Expected rates of return on plan assets			2.27	%		2.4	%		2.42	%
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	'
	The following table sets forth the combined funded status and amounts recognized in the accompanying consolidated balance sheets at March 31, 2013 and 2014 for the plans of MHFG and its subsidiaries:
			2013			2014
			(in millions of yen)
	Change in benefit obligation:
	Benefit obligation at beginning of fiscal year			1,343,714			1,399,123
	Service cost			30,422			33,429
	Interest cost			23,186			20,341
	Plan participants’ contributions			1,184			1,181
	Amendments			1,782			—
	Actuarial loss (gain)			63,140			(70,214	)
	Foreign exchange translation			2,209			4,854
	Benefits paid			(49,593	)		(49,905	)
	Lump-sum payments			(16,921	)		(18,119	)
	Benefit obligation at end of fiscal year			1,399,123			1,320,690
	Change in plan assets:
	Fair value of plan assets at beginning of fiscal year			1,323,163			1,527,744
	Actual return (negative return) on plan assets			199,341			171,970
	Foreign exchange translation			1,783			4,128
	Employer contributions			51,866			50,936
	Plan participants’ contributions			1,184			1,181
	Benefits paid			(49,593	)		(49,905	)
	Fair value of plan assets at end of fiscal year			1,527,744			1,706,054
	Funded status			128,621			385,364
	Amounts recognized in the consolidated balance sheets consist of:
	Prepaid pension cost			153,414			403,654
	Accrued pension liability			(24,793	)		(18,290	)
	Net amount recognized			128,621			385,364
	Amounts recognized in Accumulated other comprehensive income (loss) before-tax consist of:
	Prior service benefit (cost)			(440	)		(635	)
	Net actuarial gain (loss)			(236,359	)		(24,814	)
	Net amount recognized			(236,799	)		(25,449	)
	Note:	The aggregated accumulated benefit obligations of these plans were ¥1,364,786 million and ¥1,319,771 million, respectively, as of March 31, 2013 and 2014. The defined benefit plans generally employ a multi-variable and non-linear formula based upon rank and years of service. Employees with service in excess of one year are qualified to receive lump-sum severance indemnities.
Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets	'
	The following table shows the projected benefit obligations and the fair value of plan assets for the plans of MHFG and its subsidiaries with projected benefit obligations in excess of plan assets, and the accumulated benefit obligations and the fair value of plan assets for the plans with accumulated benefit obligations in excess of plan assets at March 31, 2013 and 2014:
			2013			2014
			(in millions of yen)
	Plans with projected benefit obligations in excess of plan assets:
	Projected benefit obligation			95,789			40,509
	Fair value of plan assets			70,690			21,898
	Plans with accumulated benefit obligations in excess of plan assets:
	Accumulated benefit obligation			91,210			39,590
	Fair value of plan assets			70,690			21,898
	Note:	The plans with projected benefit obligations in excess of plan assets include those with accumulated benefit obligations in excess of plan assets.
Schedule of Expected Benefit Payments	'
	The following table presents forecasted benefit payments including the effect of expected future service for the fiscal years indicated:
			(in millions of yen)
	Fiscal year ending March 31:
	2015			65,570
	2016			68,183
	2017			70,083
	2018			71,558
	2019			72,543
	2020-2024			355,295
Target Allocation	'
Schedule of Allocation of Plan Assets	'
	MHFG and certain subsidiaries’ target allocation for the plan assets excluding those of the employee retirement benefit trusts at March 31, 2014 is as follows:
	Asset category		Asset ratio
	Japanese equity securities			5	%
	Japanese debt securities			44	%
	Foreign equity securities			26	%
	Foreign debt securities			10	%
	General account of life insurance companies			14	%
	Other			1	%
	Total			100	%
	Note:	General account of life insurance companies is a contract with life insurance companies which guarantees payments of principal and predetermined interest rate.
Fair Value, Inputs	'
Schedule of Allocation of Plan Assets	'
	The following table presents the fair value of plan assets of MHFG and its subsidiaries at March 31, 2013 and 2014, by asset class. For the detailed information on fair value measurements, including descriptions of Level 1, 2 and 3 of the fair value hierarchy and the valuation methodologies, see Note 28 “Fair value”.
			2013											2014
			Level 1			Level 2			Level 3			Total		Level 1			Level 2			Level 3		Total
			(in billions of yen)
	Japanese equity securities:
	Common stocks (1)			716			—			—			716		782			—			—		782
	Pooled funds (2)			—			86			—			86		5			51			—		56
	Japanese debt securities:
	Government bonds			179			—			—			179		229			—			—		229
	Pooled funds (2)			—			46			—			46		—			68			—		68
	Other			—			7			—			7		—			24			—		24
	Foreign equity securities:
	Common stocks			54			2			—			56		96			3			—		99
	Pooled funds (2)			—			92			—			92		15			139			—		154
	Foreign debt securities:
	Government bonds			71			4			—			75		63			6			—		69
	Pooled funds (2)			—			46			—			46		—			9			—		9
	Other			—			23			—			23		—			15			—		15
	General account of life insurance			—			111			—			111		—			111			—		111
	companies (3)
	Hedge funds			—			—			1			1		—			—			2		2
	Other			92	(4)		(2	)(5)		—			90		91	(4)		(3	) (5)		—		88
	Total assets at fair value			1,112			415			1			1,528		1,281			423			2		1,706
	Notes:
	-1	This class includes equity securities held in the employee retirement benefit trusts of ¥681 billion and ¥782 billion at March 31, 2013 and 2014, respectively, which are well-diversified across industries.
	-2	These classes primarily include pension investment fund trusts. Investments in these classes are generally measured at their net asset values per share and can be redeemable within a short-term period upon request.
	-3	Investments in this class are measured at conversion value.
	-4	Amounts primarily include cash and short-term assets carried at fair value.
	-5	Amounts primarily include foreign exchange contracts carried at fair value.

Stockbased_compensation_Tables

Stock-based compensation (Tables) (Mizuho Financial Group Inc, Mizuho Bank Limited and Mizuho Corporate Bank Limited)	12 Months Ended
	Mar. 31, 2014
Mizuho Financial Group Inc, Mizuho Bank Limited and Mizuho Corporate Bank Limited	'
Schedule of Share-based Compensation, Stock Options, Activity	'
	The following is a roll-forward of MHFG Stock Plan for the fiscal year ended March 31, 2014:
		Number of			Weighted-average			Weighted-average		Aggregate
		shares			exercise price			remaining		intrinsic value
								contractual term
					(in yen)			(in years)		(in millions of yen)
	Outstanding at beginning of fiscal year		23,863,000			1
	Granted during fiscal year		7,932,000			1
	Exercised during fiscal year		9,252,000			1
	Outstanding at end of fiscal year		22,543,000			1			18.47		4,576
	Exercisable at end of fiscal year		630,000			1			16.31		128
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	'
	The expected dividend yield is based on the dividend rate of MHFG common stock at the date of grant.
		For the stock acquisition rights granted
		during the fiscal years ended March 31,
		2013			2014
	Risk-free interest rate		0.1	%		0.08	%
	Expected volatility		29.3	%		28.16	%
	Expected remaining term (in years)		2.42			2.46
	Expected dividend yield		4.69	%		3.11	%

Derivative_financial_instrumen1

Derivative financial instruments (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Derivative Instruments	'
	The following table summarizes the notional and fair value amounts of derivative instruments outstanding as of March 31, 2013 and 2014. The fair values of derivatives are presented on a gross basis and not offset against the right to reclaim cash collateral or the obligation to return cash collateral under master netting agreements in the consolidated balance sheets, or the table below.
						Fair value
						Derivative receivables (2)						Derivative payables (2)
	2013		Notional amount (1)			Designated			Not designated			Designated			Not designated
						as hedges			as hedges			as hedges			as hedges
			(in billions of yen)
	Interest rate contracts			854,698			—			10,350			—			10,018
	Foreign exchange contracts			118,708			—			3,099			10			2,973
	Equity-related contracts			3,419			—			182			—			177
	Credit-related contracts			5,266			—			59			—			44
	Other contracts			522			—			38			—			27
	Total			982,613			—			13,728			10			13,239
						Fair value
						Derivative receivables (2)						Derivative payables (2)
	2014		Notional amount (1)			Designated			Not designated			Designated			Not designated
						as hedges			as hedges			as hedges			as hedges
			(in billions of yen)
	Interest rate contracts			971,939			—			8,064			—			7,895
	Foreign exchange contracts			119,864			—			2,354			2			2,349
	Equity-related contracts			2,979			1			196			—			178
	Credit-related contracts			4,662			—			49			—			34
	Other contracts			463			—			23			—			17
	Total			1,099,907			1			10,686			2			10,473
	Notes:
	-1	Notional amount represents the sum of gross long and gross short third-party contracts.
	-2	Derivative receivables and payables are recorded in Trading account assets and Trading account liabilities, respectively.
Schedule of Net Investment Hedges, Statements of Financial Performance and Financial Position, Location	'
	The following table summarizes gains and losses information related to net investment hedges for the fiscal years ended March 31, 2012, 2013 and 2014:
			Gains (losses) recorded in income and other comprehensive income (“OCI”)
			2012						2013						2014
			Effective portion			Ineffective portion			Effective portion			Ineffective portion			Effective portion			Ineffective portion
			recorded in OCI			recorded in			recorded in OCI			recorded in			recorded in OCI			recorded in
						income						income						income
			(in millions of yen)
	Financial instruments hedging foreign exchange risk			8,024			1,666			(65,851	)		(2,908	)		(102,150	)		(7,316	)
	Total			8,024			1,666			(65,851	)		(2,908	)		(102,150	)		(7,316	)
	Note:	Related to the effective portion of net investment hedges, Accumulated other comprehensive income of ¥1,893 million and ¥13,858 million were reclassified to earnings for the fiscal years ended March 31, 2012 and 2013 respectively. No amount related to the effective portion of net investment hedges was reclassified from Accumulated other comprehensive income (loss) to earnings for the fiscal year ended March 31, 2014.
Disclosure of Credit Derivatives	'
	The following table summarizes the notional and fair value amounts of credit derivatives at March 31, 2013 and 2014:
			2013						2014
			Notional amount			Fair value			Notional amount			Fair value
			(in billions of yen)
	Credit protection written:
	Investment grade			1,810			1			1,723			21
	Non-investment grade			652			1			479			3
	Total			2,462			2			2,202			24
	Credit protection purchased			2,870			13			2,548			(9	)
	Note:	The rating scale is based upon either the external ratings or the internal ratings of the underlying reference credit. The lowest investment grade rating is considered to be BBB- or the corresponding internal rating, while anything below or unrated is considered to be non-investment grade. Non-investment grade credit derivatives primarily consist of unrated credit default swap indices such as CDX and iTraxx.
Notional And Credit Risk Amounts Of Outstanding Derivative Positions Disclosure	'
	The following table shows the maximum potential amount of future payments for credit protection written by expiration period at March 31, 2013 and 2014:
			Maximum payout/Notional amount
			2013			2014
			(in billions of yen)
	One year or less			620			325
	After one year through five years			1,720			1,791
	After five years			122			86
	Total			2,462			2,202
	Note:	The maximum potential amount of future payments is the aggregate notional amount of the credit derivatives where the Group wrote the credit protection, and it has not been reduced by the Group’s right of collection over the underlying assets and the related cash flows, nor netted against that of credit protection purchased.
Fair Value Hedging	'
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance	'
	The following table summarizes gains and losses information related to fair value hedges for the fiscal years ended March 31, 2012, 2013 and 2014:
			Gains (losses) recorded in income
	2012		Derivatives			Hedged			Hedge			Net gain (loss) excluded
						items			ineffectiveness			from assessment of
												effectiveness
			(in millions of yen)
	Interest rate contracts			(214	)		150			—			(64	)
	Equity-related contracts			(285	)		278			—			(7	)
	Total			(499	)		428			—			(71	)
			Gains (losses) recorded in income
	2013		Derivatives			Hedged			Hedge			Net gain (loss) excluded
						items			ineffectiveness			from assessment of
												effectiveness
			(in millions of yen)
	Interest rate contracts			44			(81	)		—			(37	)
	Equity-related contracts			352			(394	)		—			(42	)
	Total			396			(475	)		—			(79	)
			Gains (losses) recorded in income
	2014		Derivatives			Hedged			Hedge			Net gain (loss) excluded
						items			ineffectiveness			from assessment of
												effectiveness
			(in millions of yen)
	Equity-related contracts			801			(1,112	)		—			(311	)
	Total			801			(1,112	)		—			(311	)
Not Designated as Hedging Instrument	'
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance	'
	The following table summarizes gains and losses on derivatives not designated or qualifying as hedges during the fiscal years ended March 31, 2012, 2013 and 2014:
			Gains (losses) recorded in income
			2012			2013			2014
			(in millions of yen)
	Interest rate contracts (1)			261,632			219,422			(79,562	)
	Foreign exchange contracts			(146,258	)		(91,300	)		(13,167	)
	Equity-related contracts (1)			(7,143	)		(59,421	)		(41,296	)
	Credit-related contracts (2)			(5,575	)		(6,877	)		(7,761	)
	Other contracts			283			(2,378	)		(6,857	)
	Total			102,939			59,446			(148,643	)
	Notes:
	-1	The net gain (loss) excluded from the assessment of the effectiveness of fair value hedges is not included in the above table.
	-2	Amounts include the net loss of ¥3,391 million, ¥6,703 million and ¥8,660 million on the credit derivatives hedging the credit risk of loans during the fiscal years ended March 31, 2012, 2013 and 2014, respectively.

Commitments_and_contingencies_

Commitments and contingencies (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Guarantor Obligations	'
	The maximum exposure or notional amount below does not represent the expected losses from the execution of the guarantees.
	2013		Maximum		Amount by expiration period
			potential/Contractual
			or Notional amount		One year or less		After one year		After five years
							through
							five years
			(in billions of yen)
	Performance guarantees			1,750		935		619		196
	Guarantees on loans			452		159		51		242
	Guarantees on securities			146		19		127		—
	Other guarantees			1,068		826		217		25
	Guarantees for the repayment of trust principal			171		—		133		38
	Liabilities of trust accounts			8,606		8,428		72		106
	Derivative financial instruments			23,582		10,185		11,837		1,560
	2014		Maximum		Amount by expiration period
			potential/Contractual
			or Notional amount		One year or less		After one year		After five years
							through
							five years
			(in billions of yen)
	Performance guarantees			1,985		1,125		708		152
	Guarantees on loans			399		173		21		205
	Guarantees on securities			170		42		128		—
	Other guarantees			1,249		991		220		38
	Guarantees for the repayment of trust principal			158		—		125		33
	Liabilities of trust accounts			11,158		10,962		78		118
	Derivative financial instruments			21,422		8,643		11,391		1,388
	The table below presents the maximum potential amount of future payments of performance guarantees, guarantees on loans, guarantees on securities and other guarantees classified based on internal ratings at March 31, 2013 and 2014:
			2013		2014
			(in billions of yen)
	Investment grade			2,387		2,673
	Non-investment grade			1,029		1,130
	Total			3,416		3,803
	Note:	Investment grade in the internal rating scale generally corresponds to BBB- or above in external rating scale.
Schedule of Off Balance Sheet Commitments and Guarantees	'
	The table below summarizes the contractual amounts with regard to these undrawn commitments at March 31, 2013 and 2014:
			2013		2014
			(in billions of yen)
	Commitments to extend credit (Note)			59,101		59,402
	Commercial letters of credit			608		611
	Total			59,709		60,013
	Note: Commitments to extend credit include commitments to invest in securities.
Future Minimum Lease Payments for Capitalized Leases and Rental Payments for Operating Leases	'
	Future minimum lease payments for capitalized leases and future minimum rental payments for operating leases at March 31, 2014 were as follows:
			Capitalized leases		Operating leases
			(in millions of yen)
	Fiscal year ending March 31:
	2015			6,479		48,233
	2016			5,929		40,195
	2017			5,186		35,584
	2018			4,547		31,556
	2019			3,820		29,237
	2020 and thereafter			2,068		74,596
	Total minimum lease/rental payments			28,029		259,401
	Amount representing interest			1,349
	Present value of minimum lease payments			26,680

Variable_interest_entities_and1

Variable interest entities and securitizations (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Variable Interest Entities	'
	The tables below show consolidated assets of the Group’s consolidated VIEs as well as total assets and maximum exposure to loss for its significant unconsolidated VIEs, as of March 31, 2013 and 2014:
		Consolidated VIEs		Significant
				unconsolidated VIEs
	2013	Consolidated assets		Total assets		Maximum
						exposure to loss
		(in billions of yen)
	Asset-backed commercial paper/loan programs		2,212		—		—
	Asset-backed securitizations		385		463		37
	Investments in securitization products		—		530		206
	Investment funds		1,175		2,770		302
	Trust arrangements and other		39		—		—
	Total		3,811		3,763		545
		Consolidated VIEs		Significant
				unconsolidated VIEs
	2014	Consolidated assets		Total assets		Maximum
						exposure to loss
		(in billions of yen)
	Asset-backed commercial paper/loan programs		2,403		—		—
	Asset-backed securitizations		423		385		39
	Investments in securitization products		181		531		200
	Investment funds		1,508		2,935		387
	Trust arrangements and other		38		—		—
	Total		4,553		3,851		626
Unconsolidated VIEs	'
Schedule of Variable Interest Entities	'
	The tables below present the carrying amounts and classification of assets and liabilities on the MHFG Group’s balance sheets that relate to its variable interests in the significant unconsolidated VIEs, as of March 31, 2013 and 2014:
	Assets on balance sheets related to unconsolidated VIEs:	2013		2014
		(in billions of yen)
	Trading account assets		46		29
	Investments		206		222
	Loans		308		316
	Total		560		567
	Liabilities on balance sheets and maximum exposure to loss related to unconsolidated VIEs:	2013		2014
		(in billions of yen)
	Payables under securities lending transactions		14		4
	Total		14		4
	Maximum exposure to loss		545		626

Fees_and_commissions_income_Ta

Fees and commissions income (Tables)	12 Months Ended
	Mar. 31, 2014
Other Income and Other Expense Disclosure	'
	Details of Fees and commissions income for the fiscal years ended March 31, 2012, 2013 and 2014 are as follows:
		2012		2013		2014
		(in millions of yen)
	Securities-related business		116,567		132,787		170,311
	Deposits, debentures and lending business		97,509		113,989		114,073
	Remittance business		105,015		104,574		108,534
	Trust fees		45,990		45,621		48,914
	Fees for other customer services		210,332		215,837		233,931
	Total		575,413		612,808		675,763

Trading_account_gains_and_loss1

Trading account gains and losses (Tables)	12 Months Ended
	Mar. 31, 2014
Gain (Loss) on Investments	'
	Net trading gains (losses) for the fiscal years ended March 31, 2012, 2013 and 2014 are comprised of the following:
			2012			2013			2014
			(in millions of yen)
	Trading account gains (losses)—net:
	Trading securities			227,056			468,029			80,606
	Derivative contracts:
	Interest rate contracts (1)			261,568			219,385			(79,562	)
	Foreign exchange contracts			(146,258	)		(91,300	)		(13,167	)
	Equity-related contracts (1)			(7,150	)		(59,462	)		(41,607	)
	Credit-related contracts (2)			(2,184	)		(174	)		899
	Other contracts			283			(2,378	)		(6,856	)
	Total			333,315			534,100			(59,687	)
	Foreign exchange gains (losses)—net (3)			98,054			20,514			25,631
	Net trading gains (losses)			431,369			554,614			(34,056	)
	Notes:
	-1	The net gain (loss) excluded from the assessment of the effectiveness of fair value hedges is included in the above table.
	-2	Amounts do not include the net loss of ¥3,391 million, ¥6,703 million and ¥8,660 million on the credit derivatives hedging the credit risk of loans during the fiscal years ended March 31, 2012, 2013 and 2014, respectively. The net loss is recorded in Other noninterest expenses.
	-3	Amounts include realized and unrealized gains and losses on both derivative instruments and nonderivative instruments, such as translation gains and losses related to foreign currency-denominated available-for-sale securities for which the fair value option is elected in accordance with ASC 825.

Fair_value_Tables

Fair value (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	'
	Assets and liabilities measured at fair value on a recurring basis at March 31, 2013 and 2014, including those for which the MHFG Group has elected the fair value option, are summarized below:
	2013		Level 1			Level 2			Level 3			Assets/
												Liabilities
												measured
												at fair value
			(in billions of yen)
	Assets:
	Trading securities (1):
	Japanese government bonds			4,651			49			—			4,700
	Japanese local government bonds			—			125			—			125
	U.S. Treasury bonds and federal agency securities			5,777			306			—			6,083
	Other foreign government bonds			2,235			194			—			2,429
	Agency mortgage-backed securities			2,055			596			—			2,651
	Residential mortgage-backed securities			—			—			100			100
	Commercial mortgage-backed securities			—			3			91			94
	Certificates of deposit and commercial paper			—			1,318			—			1,318
	Corporate bonds and other			50			1,176			417			1,643
	Equity securities			622			503			71			1,196
	Derivatives:
	Interest rate contracts			7			10,319			24			10,350
	Foreign exchange contracts			5			3,066			28			3,099
	Equity-related contracts			45			114			23			182
	Credit-related contracts			—			30			29			59
	Other contracts			—			18			20			38
	Available-for-sale securities:
	Japanese government bonds			29,198			1,585			—			30,783
	Japanese local government bonds			—			244			—			244
	U.S. Treasury bonds and federal agency securities			178			—			—			178
	Other foreign government bonds			334			264			—			598
	Agency mortgage-backed securities			144			862			—			1,006
	Residential mortgage-backed securities			—			150			292			442
	Commercial mortgage-backed securities			—			—			250			250
	Japanese corporate bonds and other debt securities			—			2,000			215			2,215
	Foreign corporate bonds and other debt securities			12			345			202			559
	Equity securities (marketable)			2,975			164			—			3,139
	Other investments			1			—			75			76
	Total assets measured at fair value on a recurring basis (2)			48,289			23,431			1,837			73,557
	Liabilities:
	Trading securities sold, not yet purchased			3,338			182			—			3,520
	Derivatives:
	Interest rate contracts			8			9,997			13			10,018
	Foreign exchange contracts			4			2,968			11			2,983
	Equity-related contracts			51			110			16			177
	Credit-related contracts			—			35			9			44
	Other contracts			—			8			19			27
	Long-term debt (3)			—			171			381			552
	Total liabilities measured at fair value on a recurring basis			3,401			13,471			449			17,321
	2014		Level 1			Level 2			Level 3			Assets/
												Liabilities
												measured
												at fair value
			(in billions of yen)
	Assets:
	Trading securities (1):
	Japanese government bonds			3,360			50			—			3,410
	Japanese local government bonds			—			74			—			74
	U.S. Treasury bonds and federal agency securities			3,541			486			—			4,027
	Other foreign government bonds			2,567			274			—			2,841
	Agency mortgage-backed securities			1,390			364			—			1,754
	Residential mortgage-backed securities			—			—			78			78
	Commercial mortgage-backed securities			—			2			91			93
	Certificates of deposit and commercial paper			—			969			—			969
	Corporate bonds and other			38			1,671			413			2,122
Equity securities			714			579			60			1,353
Derivatives:
Interest rate contracts			43			7,997			24			8,064
Foreign exchange contracts			6			2,331			17			2,354
Equity-related contracts			60			124			13			197
Credit-related contracts			—			28			21			49
Other contracts			1			18			4			23
Available-for-sale securities:
Japanese government bonds			20,912			1,144			—			22,056
Japanese local government bonds			—			245			—			245
U.S. Treasury bonds and federal agency securities			154			—			—			154
Other foreign government bonds			280			441			—			721
Agency mortgage-backed securities			105			856			—			961
Residential mortgage-backed securities			—			112			220			332
Commercial mortgage-backed securities			—			—			161			161
Japanese corporate bonds and other debt securities			—			1,858			170			2,028
Foreign corporate bonds and other debt securities			1			427			141			569
Equity securities (marketable)			3,348			74			—			3,422
Other investments			2			—			69			71
Total assets measured at fair value on a recurring basis (2)			36,522			20,124			1,482			58,128
Liabilities:
Trading securities sold, not yet purchased			3,862			488			—			4,350
Derivatives:
Interest rate contracts			42			7,846			7			7,895
Foreign exchange contracts			5			2,340			6			2,351
Equity-related contracts			58			108			12			178
Credit-related contracts			—			30			4			34
Other contracts			1			12			4			17
Long-term debt (3)			—			157			501			658
Total liabilities measured at fair value on a recurring basis			3,968			10,981			534			15,483
Notes:
-1	Trading securities include foreign currency denominated securities for which the MHFG Group elected the fair value option.
-2	Amounts include the investments measured at the NAV per share at March 31, 2013 and 2014, of ¥715 billion and ¥649 billion, respectively, of which ¥667 billion and ¥612 billion, respectively, are classified in Level 2, and ¥48 billion and ¥37 billion, respectively, are classified in Level 3. The amounts of unfunded commitments related to these investments at March 31, 2013 and 2014 were ¥24 billion and ¥23 billion, respectively.
-3	Amounts represent items for which the Group elected the fair value option.
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	'
	The following table presents a reconciliation for all assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the fiscal years ended March 31, 2013 and 2014:
	2013		April 1,			Gains			Gains			Transfers			Transfers			Purchases			Sales			Issuances		Settlements			March 31,		Change in
			2012			(losses) in			(losses)			into			out of														2013		unrealized
						Earnings			in OCI			Level 3			Level 3																gains
																															(losses)
																															still held (6)
			(in billions of yen)
	Assets:
	Trading securities:
	Residential mortgage-			159			17	(2)		—			—			—			2			(7	)		—		(71	)		100		6
	backed securities
	Commercial mortgage-			26			1	(2)		—			—			—			72			(1	)		—		(7	)		91		—
	backed securities
	Corporate bonds and other			355			72	(2)		—			14			(8	)		609			(544	)		—		(81	)		417		42
	Equity securities			82			4	(2)		—			3			(3	)		10			(25	)		—		—			71		(1	)
	Derivatives, net (1):
	Interest rate contracts			(10	)		16	(2)		—			—			—			—			—			—		5			11		16
	Foreign exchange contracts			37			(18	)(2)		—			—			(8	)		—			—			—		6			17		(21	)
	Equity-related contracts			22			(10	)(2)		—			—			—			—			—			—		(5	)		7		(10	)
	Credit-related contracts			23			(6	)(2)		—			(1	)		1			—			—			—		3			20		(5	)
	Other contracts			15			—	(2)		—			—			(14	)		—			—			—		—			1		—
	Available-for-sale securities:
	Residential mortgage-			348			—	(3)		6	(4)		—			—			29			(1	)		—		(90	)		292		—
	backed securities
	Commercial mortgage-			330			2	(3)		12	(4)		—			—			31			(16	)		—		(109	)		250		(5	)
	backed securities
	Japanese corporate			226			—	(3)		1	(4)		—			—			95			—			—		(107	)		215		—
	bonds and other debt securities
	Foreign corporate bonds			236			4	(3)		6	(4)		—			—			28			(4	)		—		(68	)		202		—
	and other debt securities
	Other investments			189			12	(3)		—			—			—			6			(49	)		—		(83	)		75		—
	Liabilities:
	Trading securities sold, not yet purchased			—			—	(2)		—			—			(1	)		(41	)		42			—		—			—		—
	Long-term debt			460			(26	)(5)		—			4			(175	)		—			—			142		(76	)		381		(24	)
	2014		April 1,			Gains			Gains			Transfers			Transfers			Purchases			Sales			Issuances		Settlements			March 31,		Change in
			2013			(losses) in			(losses)			into			out of														2014		unrealized
						Earnings			in OCI			Level 3			Level 3																gains
																															(losses)
																															still held (6)
			(in billions of yen)
	Assets:
	Trading securities:
	Residential mortgage-backed securities			100			10	(2)		—			—			—			—			(4	)		—		(28	)		78		7
	Commercial mortgage-backed securities			91			5	(2)		—			—			—			—			—			—		(5	)		91		4
	Corporate bonds and other			417			55	(2)		—			4			(12	)		503			(442	)		—		(112	)		413		35
	Equity securities			71			6	(2)		—			—			—			8			(24	)		—		(1	)		60		—
	Derivatives, net (1):
	Interest rate contracts			11			6	(2)		—			(1	)		—			—			—			—		1			17		11
	Foreign exchange contracts			17			(3	)(2)		—			—			—			—			—			—		(3	)		11		5
	Equity-related contracts			7			(6	)(2)		—			—			—			—			—			—		—			1		(7	)
	Credit-related			20			(6	)(2)		—			—			1			—			—			—		2			17		(6	)
	contracts
	Other contracts			1			—	(2)		—			—			—			—			—			—		(1	)		—		—
	Available-for-sale securities:
	Residential mortgage-backed securities			292			(1	)(3)		5	(4)		—			—			5			(9	)		—		(72	)		220		—
	Commercial mortgage-backed securities			250			5	(3)		(2	)(4)		—			—			36			(18	)		—		(110	)		161		(1	)
	Japanese corporate			215			—	(3)		—	(4)		—			(30	)		60			(1	)		—		(74	)		170		—
	bonds and other debt securities
	Foreign corporate bonds and other debt securities			202			8	(3)		(1	)(4)		7			—			—			—			—		(75	)		141		—
	Other investments			75			(2	)(3)		—			—			(2	)		7			(2	)		—		(7	)		69		(2	)
	Liabilities:
	Long-term debt			381			4	(5)		—			1			(1	)		—			—			197		(73	)		501		5
	Notes:
-1	Total Level 3 derivative exposures have been netted on the table for presentation purposes only.
-2	Gains (losses) in Earnings are reported in Trading account gains (losses)—net, Foreign exchange gains (losses)—net or Other noninterest income (expenses).
-3	Gains (losses) in Earnings are reported in Investment gains (losses)—net.
-4	Gains (losses) in OCI are reported in Accumulated other comprehensive income (loss).
-5	Gains (losses) in Earnings are reported in Other noninterest income (expenses).
-6	Amounts represent total gains or losses recognized in earnings during the period. These gains or losses are attributable to the change in fair value relating to assets and liabilities classified as Level 3 that are still held at March 31, 2013 and 2014.
Quantitative Information About Level Three Fair Value Measurements	'
	The following table presents information about significant unobservable inputs related to the MHFG Group’s material classes of Level 3 assets and liabilities at March 31, 2013 and 2014:
	2013
	Products/Instruments		Fair value			Principal valuation technique		Unobservable inputs	Range of input values
	(in billions of yen, except for ratios and basis points)
	Trading securities and Available-for-sale securities:
	Residential mortgage-backed securities			392		Discounted cash flow		Prepayment rate		0%–24%
						Price-based		Default rate		0%–5%
								Recovery rate		70%–100%
								Discount margin		7bps–2,616bps
	Commercial mortgage-backed securities			341		Discounted cash flow		Discount margin		9bps–3,929bps
						Price-based
	Corporate bonds and other debt securities			834		Discounted cash flow		Prepayment rate (1)		0%–43%
						Price-based		Default rate (1)		0%–8%
								Recovery rate (1)		15%–85%
								Discount margin (1)		0bps–4,918bps
								Discount margin (2)		0bps–1,232bps
	Derivatives, net:
	Interest rate contracts			11		Internal valuation model (3)		IR – IR correlation		42%–100%
								Default rate (4)		0%–63%
	Foreign exchange contracts			17		Internal valuation model (3)		FX – IR correlation		36%–55%
								FX – FX correlation		55%–55%
								FX volatility		16%–26%
								Default rate (4)		0%–63%
	Equity-related contracts			7		Internal valuation model(3)		Equity – IR correlation		0%–60%
								Equity – FX correlation		0%–70%
								Equity volatility		14%–48%
	Credit-related contracts (5)			20		Internal valuation model (3)		Default rate		0%–67%
								Credit correlation		2%–100%
	Long-term debt			381		Internal valuation model (3)		IR – IR correlation		42%–100%
								FX – IR correlation		36%–55%
								FX – FX correlation		55%–55%
								Equity – IR correlation		0%–60%
								Equity volatility		18%–48%
								Default rate		0%–10%
								Credit correlation		2%–100%
	2014
	Products/Instruments		Fair value			Principal valuation technique		Unobservable inputs	Range of input values
	(in billions of yen, except for ratios and basis points)
	Trading securities and Available-for-sale securities:
	Residential mortgage-backed securities			298		Discounted cash flow		Prepayment rate		1%–24%
						Price-based		Default rate		0%–4%
								Recovery rate		70%–100%
								Discount margin		8bps–2,002bps
	Commercial mortgage-backed securities			252		Discounted cash flow		Discount margin		17bps – 3,441bps
						Price-based
	Corporate bonds and other debt securities			724		Discounted cash flow		Prepayment rate (1)		0%–42%
						Price-based		Default rate (1)		0%–9%
								Recovery rate (1)		15%–75%
								Discount margin (1)		12bps–1,725bps
								Discount margin (2)		-122bps–1,303bps
	Derivatives, net:
	Interest rate contracts			17		Internal valuation model (3)		IR – IR correlation		23%–100%
								Default rate (4)		0%–63%
	Foreign exchange contracts			11		Internal valuation model (3)		FX – IR correlation		28%–52%
								FX – FX correlation		55%–55%
								FX volatility		14%–25%
								Default rate (4)		0%–63%
	Equity-related contracts			1		Internal valuation model (3)		Equity – IR correlation		0%–60%
								Equity – FX correlation		0%–70%
								Equity volatility		18%–35%
	Credit-related contracts (5)			17		Internal valuation model (3)		Default rate		0%–47%
								Credit correlation		1%–100%
	Long-term debt			501		Internal valuation model (3)		IR – IR correlation		23%–100%
							FX – IR correlation		28%–52%
							FX – FX correlation		55%–55%
							Equity – IR correlation		0%–60%
							Equity – FX correlation		0%–70%
							Equity volatility		13%–37%
							Default rate		0%–5%
							Credit correlation		19%–100%
Notes:
-1	These inputs are mainly used for determining the fair values of securitization products such as CDO, CLO and ABS, other than RMBS and CMBS.
-2	This input is mainly used for determining the fair values of Japanese corporate bonds and foreign corporate bonds.
-3	Internal valuation model includes discounted cash flow models and the Black-Scholes option pricing model.
-4	This input represents the counterparty default rate derived from the MHFG Group’s own internal credit analysis.
-5	The majority of the fair value of credit derivatives in Level 3 relates to credit derivatives economically hedging the credit risk in certain securitization products. The unobservable inputs of these credit derivatives have already been included in the unobservable inputs related to Trading securities and Available-for-sale securities disclosed above.
IR =nterest rate
FX =oreign exchange
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis	'
	The following table shows the fair value hierarchy for these items as of March 31, 2013 and 2014.
	2013		Total			Level 1			Level 2			Level 3			Aggregate cost
			(in billions of yen)
	Assets:
	Loans			222			—			—			222			343
	Loans held-for-sale			5			—			5			—			5
	Other investments			11			—			—			11			16
	Premises and equipment—net			1			—			—			1			5
	Total assets at fair value on a nonrecurring basis			239			—			5			234			369
	2014		Total			Level 1			Level 2			Level 3			Aggregate cost
			(in billions of yen)
	Assets:
	Loans			124			—			—			124			208
	Loans held-for-sale			33			—			—			33			34
	Other investments			5			—			—			5			6
	Premises and equipment—net			1			—			—			1			2
	Goodwill			—			—			—			—			4
	Total assets at fair value on a nonrecurring basis			163			—			—			163			254
Fair Value, by Balance Sheet Grouping	'
	The following table shows the carrying amounts and fair values at March 31, 2013 and 2014, of certain financial instruments, excluding financial instruments which are carried at fair value on a recurring basis and those outside the scope of ASC 825 such as the equity method investments and lease contracts as defined in ASC 840, “Leases” (“ASC 840”) :
			2013
			Carrying			Estimated fair value
			amount			Total			Level 1			Level 2			Level 3
			(in billions of yen)
	Financial assets:
	Cash and due from banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions			27,583			27,583			903			26,680			—
	Investments			3,000			3,020			3,020			—			—
	Loans, net of allowance for loan losses (Note)			69,028			70,261			—			—			70,261
	Financial liabilities:
	Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions			48,048			48,048			12,796			35,252			—
	Interest-bearing deposits			87,247			87,210			34,596			52,614			—
	Due to trust accounts			619			619			—			619			—
	Other short-term borrowings			6,724			6,723			—			6,723			—
	Long-term debt			8,235			8,598			—			7,967			631
			2014
			Carrying			Estimated fair value
			amount			Total			Level 1			Level 2			Level 3
			(in billions of yen)
	Financial assets:
	Cash and due from banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions			34,563			34,563			1,437			33,126			—
	Investments			4,040			4,058			4,058			—			—
	Loans, net of allowance for loan losses (Note)			72,801			73,975			—			—			73,975
	Financial liabilities:
	Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions			44,124			44,124			13,543			30,581			—
	Interest-bearing deposits			88,744			88,705			37,394			51,311			—
	Due to trust accounts			742			742			—			742			—
	Other short-term borrowings			6,024			6,024			—			6,024			—
	Long-term debt			9,176			9,441			—			8,600			841
	Note: Loans, net of allowance for loan losses include items measured at fair value on a nonrecurring basis.

Offsetting_of_financial_assets1

Offsetting of financial assets and financial liabilities (Tables)	12 Months Ended
	Mar. 31, 2014
Information of Offsetting of Financial Assets and Financial Liabilities	'
	The following tables provide information about the offsetting of financial assets and financial liabilities at March 31, 2013 and 2014. The tables include derivatives, repurchase and resale agreements, and securities lending and borrowing transactions that are subject to enforceable master netting arrangements or similar agreements irrespective of whether or not they are offset on the Group’s consolidated balance sheets.
									Amounts not offset on
									the balance sheet(3)
			Gross amounts		Gross amounts		Net amounts		Financial		Cash		Net
			recognized		offset on the		presented on the		instruments(4)		collateral		amounts
					balance sheet		balance sheet(2)
			(in billions of yen)
	2013
	Assets (1):
	Derivatives			13,019		—		13,019		11,289		446		1,284
	Receivables under resale agreements			8,869		—		8,869		8,812		—		57
	Receivables under securities borrowing transactions			5,544		—		5,544		5,534		—		10
	Total			27,432		—		27,432		25,635		446		1,351
	Liabilities (1):
	Derivatives			12,712		—		12,712		11,234		653		825
	Payables under repurchase agreements			17,397		—		17,397		17,280		—		117
	Payables under securities lending transactions			11,326		—		11,326		11,320		—		6
	Total			41,435		—		41,435		39,834		653		948
	2014
	Assets (1):
	Derivatives			9,880		—		9,880		8,702		406		772
	Receivables under resale agreements			8,236		—		8,236		8,200		—		36
	Receivables under securities borrowing transactions			4,990		—		4,990		4,978		—		12
	Total			23,106		—		23,106		21,880		406		820
	Liabilities (1):
	Derivatives			9,648		—		9,648		8,621		431		596
	Payables under repurchase agreements			16,690		—		16,690		16,667		—		23
	Payables under securities lending transactions			6,085		—		6,085		6,082		—		3
	Total			32,423		—		32,423		31,370		431		622
	Notes:
	-1	Amounts relating to master netting arrangements or similar agreements where the Group does not have the legal right of set-off or where uncertainty exists as to the enforceability of these agreements are excluded. For derivatives, the table includes amounts relating to over-the-counter (“OTC”) and OTC-cleared derivatives that are subject to enforceable master netting arrangements or similar agreements.
	-2	Derivative assets and liabilities are recorded in Trading account assets and Trading account liabilities, respectively.
	-3	Amounts do not exceed the net amounts presented on the balance sheet and do not include the effect of overcollateralization, where it exists.
	-4	For derivatives, amounts include derivative assets or liabilities and securities collateral that are eligible for offsetting under enforceable master netting arrangements or similar agreements.

Business_segment_information_T

Business segment information (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Segment Reporting Information, by Segment	'
	The information below for reportable segments is derived from the internal management reporting systems. Management does not use information on segments’ assets to allocate resources and assess performance and has not prepared information on segment assets. Accordingly, information on segment assets is not available.
			The former MHBK (Consolidated)
						The former MHBK (Non-consolidated)																		The former			Others
																								MHIS
																								(Consolidated)
	2012(1)		Total			Total			Personal			Retail			Corporate		Corporate		Financial		Trading			(g)			(h)
									Banking			Banking			Banking		Banking		Institution		and
									(a)			(b)			(Large		(d)		& Public		others
															Corporations)				Sector		(f)
															(c)				Business
																			(e)
			(in billions of yen)
	Gross profits:
	Net interest income (expense)			583.9			545.4			224.3			95.1			17.8		118.6		22.2		67.4			0.7			37.8
	Net noninterest income			305.8			253.3			32.1			41			19		68.2		8.6		84.4			43.9			8.6
	Total			889.7			798.7			256.4			136.1			36.8		186.8		30.8		151.8			44.6			46.4
	General and administrative			608.5			556.4			218.6			108.2			18.5		86.4		14.5		110.2			40.9			11.2
	expenses
	Others			(14.0	)		—			—			—			—		—		—		—			—			(14.0	)
	Net business profits (losses)			267.2			242.3			37.8			27.9			18.3		100.4		16.3		41.6			3.7			21.2
			The former MHCB (Consolidated)																								MHTB			Others			MHFG
																											(Consolidated)						(Consolidated)
						The former MHCB (Non-consolidated)															The former			Others
																					MHSC
																					(Consolidated)
	2012(1)		Total			Total			Corporate			Corporate			Financial		Inter-		Trading		(n)			(o)			(p)			(q)			Total
									Banking			Banking			Institution		national		and
									(Large			(j)			& Public		Banking		others
									Corporations)						Sector		(l)		(m)
									(i)						Business
															(k)
	(in billions of yen)
	Gross profits:
	Net interest income (expense)			468.3			395			150.6			2.7			18.1		90.3		133.3		(8.1	)		81.4			42.5			(6.4	)		1,088.30
	Net noninterest income			449.4			286.8			114.4			1.1			15.8		86.9		68.6		151.7			10.9			104.8			54.8			914.8
	Total			917.7			681.8			265			3.8			33.9		177.2		201.9		143.6			92.3			147.3			48.4			2,003.10
	General and administrative			465.4			244.9			75.6			1.3			11.6		60.3		96.1		192.9			27.6			92.3			40.1			1,206.30
	expenses
	Others			(52.1	)		—			—			—			—		—		—		(0.1	)		(52.0	)		(3.7	)		(7.9	)		(77.7	)
	Net business profits (losses)			400.2			436.9			189.4			2.5			22.3		116.9		105.8		(49.4	)		12.7			51.3			0.4			719.1
			The former MHBK (Consolidated)
						The former MHBK (Non-consolidated)																		Others
	2013(1)(2)(4)		Total			Total			Personal			Retail			Corporate		Corporate		Financial		Trading			(g)
									Banking			Banking			Banking		Banking		Institution		and
									(a)			(b)			(Large		(d)		& Public		others
															Corporations)				Sector		(f)
															(c)				Business
																			(e)
			(in billions of yen)
	Gross profits:
	Net interest income (expense)			550.6			513.8			219.2			83.3			14.9		106.1		19.9		70.4			36.8
	Net noninterest income			360.3			313.7			33.9			42.3			19.3		70.7		11		136.5			46.6
	Total			910.9			827.5			253.1			125.6			34.2		176.8		30.9		206.9			83.4
	General and administrative			568.2			524.4			218.6			113.7			11.6		73.2		14.3		93			43.8
	expenses
	Others			(7.4	)		—			—			—			—		—		—		—			(7.4	)
	Net business profits (losses)			335.3			303.1			34.5			11.9			22.6		103.6		16.6		113.9			32.2
	2013(1)(2)(4)		The former MHCB (Consolidated)																								MHTB			Others			MHFG
																											(Consolidated)						(Consolidated)
						The former MHCB (Non-consolidated)															MHSC			Others
																					(Consolidated)
			Total			Total			Corporate			Corporate			Financial		Inter-		Trading		(m)			(n)			(o)			(p)			Total
									Banking			Banking			Institution		national		and
(Large									(i)			& Public			Banking		others
Corporations)												Sector			(k)		(l)
(h)												Business
												(j)
(in billions of yen)
Gross profits:
Net interest income (expense)			486.1			401.7			140.9			0.5			16.3		108.2		135.8		(1.8	)		86.2			39.5			(0.3	)		1,075.90
Net noninterest income			572.8			333.4			103.3			0.2			13.2		104.7		112		229			10.4			105			57.7			1,095.80
Total			1,058.90			735.1			244.2			0.7			29.5		212.9		247.8		227.2			96.6			144.5			57.4			2,171.70
General and administrative			471.9			241.1			76.8			1.3			12.2		66.6		84.2		197.1			33.7			90.1			40.8			1,171.00
expenses
Others			(50.0	)		—			—			—			—		—		—		—			(50.0	)		(3.5	)		(27.6	)		(88.5	)
Net business profits (losses)			537			494			167.4			(0.6	)		17.3		146.3		163.6		30.1			12.9			50.9			(11.0	)		912.2
2014(1)(2)(3)(4)		MHBK (Consolidated)																											MHTB			MHSC			Others			MHFG
																													(Consolidated)			(Consolidated)						(Consolidated)
					MHBK (Non-consolidated)																					Others
		Total			Total			Personal			Retail			Corporate		Corporate		Financial		Inter-			Trading			(h)			(i)			(j)			(k)			Total
								Banking			Banking			Banking		Banking		Institution		national			and
								(a)			(b)			(Large		(d)		& Public		Banking			others
														Corporations)				Sector		(f)			(g)
														(c)				Business
																		(e)
(in billions of yen)
Gross profits:
Net interest income			933.8			800.1			165			59.8			170.2		77.9		30.7		128.9			167.6			133.7			40.2			2.9			131.4			1,108.30
Net noninterest income (expenses)			407.4			398.2			32.9			34.8			126.7		51.8		20.1		139.8			(7.9	)		9.2			108.1			283.9			127.6			927
Total			1,341.20			1,198.30			197.9			94.6			296.9		129.7		50.8		268.7			159.7			142.9			148.3			286.8			259			2,035.30
General and administrative			711.3			659			171.3			87.8			83.8		58.8		25.1		82.5			149.7			52.3			90.9			246.2			180.9			1,229.30
expenses
Others			(56.1	)		—			—			—			—		—		—		—			—			(56.1	)		(2.9	)		—			(2.7	)		(61.7	)
Net business profits			573.8			539.3			26.6			6.8			213.1		70.9		25.7		186.2			10			34.5			54.5			40.6			75.4			744.3
Notes:
-1	As for the fiscal year ended March 31, 2012, “Others (h)”, “Others (o)”, and “Others (q)” include elimination of transactions between consolidated subsidiaries. As for the fiscal year ended March 31, 2013, “Others (g)”, “Others (n)”, and “Others (p)” include elimination of transactions between consolidated subsidiaries. As for the fiscal year ended March 31, 2014, “Others (h)” and “Others (k)” include elimination of transactions between consolidated subsidiaries.
-2	Beginning on April 1, 2013, the MHFG Group moved to a new group operational structure and realigned the reportable segments to reflect the new organizational structure. In addition, new allocation methods have been applied to the calculation of “Gross profits” and “General and administrative expenses”. Figures for the fiscal year ended March 31, 2013 have been reclassified under the new allocation methods. The effect of the change of allocation methods is not significant.
-3	As for the fiscal year ended March 31, 2014, “MHBK (Non-consolidated)” represents the sum of the performance of the former MHCB for the first quarter and the new MHBK for the second, third, and fourth quarters, while “Others (h)” includes the performance of the former MHBK for the first quarter, in light of the merger of the former MHBK and the former MHCB conducted in July 2013.
-4	Beginning on April 1, 2013, MHSC was turned into a directly-held subsidiary of MHFG. As for the fiscal year ended March 31, 2013, “MHSC (Consolidated) (m)” represents the performance of the former MHSC for the first three quarters and the new MHSC for the fourth quarter, while “Others (g)” includes the performance of the former MHIS for the first three quarters. As for the fiscal year ended March 31, 2014, “MHSC (Consolidated) (j)” represents the performance of the new MHSC, in light of the merger of the former MHSC and the former MHIS conducted in January 2013.
Aggregation of MHBK and MHCB
2012		MHBK and MHCB
		Personal			Retail			Corporate			Corporate			Financial		International		Trading		Total
		Banking			Banking			Banking			Banking			Institution		Banking		and
		(a)			(b)			(Large			(d)			& Public		(f)		others
								Corporations)						Sector				(g)
								(c)						Business
														(e)
		(in billions of yen)
Gross profits:
Net interest income			224.3			95.1			168.4			121.3			40.3		90.3		200.7		940.4
Net noninterest income			32.1			41			133.4			69.3			24.4		86.9		153		540.1
Total			256.4			136.1			301.8			190.6			64.7		177.2		353.7		1,480.50
General and administrative expenses			218.6			108.2			94.1			87.7			26.1		60.3		206.3		801.3
Others			—			—			—			—			—		—		—		—
Net business profits			37.8			27.9			207.7			102.9			38.6		116.9		147.4		679.2
2013		MHBK and MHCB
		Personal			Retail			Corporate			Corporate			Financial		International		Trading		Total
		Banking			Banking			Banking			Banking			Institution		Banking		and
		(a)			(b)			(Large			(d)			& Public		(f)		others
								Corporations)						Sector				(g)
								(c)						Business
														(e)
		(in billions of yen)
Gross profits:
Net interest income			219.2			83.3			155.8			106.6			36.2		108.2		206.2		915.5
Net noninterest income			33.9			42.3			122.6			70.9			24.2		104.7		248.5		647.1
Total			253.1			125.6			278.4			177.5			60.4		212.9		454.7		1,562.60
General and administrative expenses			218.6			113.7			88.4			74.5			26.5		66.6		177.2		765.5
Others			—			—			—			—			—		—		—		—
Net business profits			34.5			11.9			190			103			33.9		146.3		277.5		797.1
2014		MHBK and MHCB
		Personal			Retail			Corporate			Corporate			Financial		International		Trading		Total
		Banking			Banking			Banking			Banking			Institution		Banking		and
		(a)			(b)			(Large			(d)			& Public		(f)		others
								Corporations)						Sector				(g)
								(c)						Business
														(e)
		(in billions of yen)
Gross profits:
Net interest income			218.5			80			172.7			103.3			35.4		128.9		185		923.8
Net noninterest income			41.6			45.3			131.4			64.7			22.3		139.8		15.2		460.3
Total			260.1			125.3			304.1			168			57.7		268.7		200.2		1,384.10
General and administrative expenses			226.4			116.7			87.2			77.7			29		82.5		171.6		791.1
Others			—			—			—			—			—		—		—		—
Net business profits			33.7			8.6			216.9			90.3			28.7		186.2		28.6		593
Note:	The former MHBK and the former MHCB merged on July 1, 2013. Figures for the fiscal years ended March 31, 2012 and 2013 represent the simple aggregation of the performance of the former MHBK and the former MHCB, and figures for the fiscal year ended March 31, 2014 represent the simple aggregation of the performance of the former MHBK and the former MHCB for the first quarter, and the new MHBK for the second, third, and fourth quarters. Beginning on April 1, 2013, the MHFG Group moved to a new group operational structure and realigned the reportable segments to reflect the new organizational structure. In addition, new allocation methods have been applied to the calculation of “Gross profits” and “General and administrative expenses”. Figures for the fiscal year ended March 31, 2013 have been reclassified under the new allocation methods.
Reconciliation of Operating Profit (Loss) from Segments to Consolidated	'
	A reconciliation of total net business profits under the internal management reporting system for the fiscal years ended March 31, 2012, 2013, and 2014 presented above to Income before income tax expense shown on the consolidated statements of income is as follows:
			2012			2013			2014
			(in billions of yen)
	Net business profits			719.1			912.2			744.3
	U.S. GAAP adjustments			87.2			129.2			(325.4	)
	(Provision) credit for loan losses			23			(139.9	)		126.2
	Net gains (losses) related to equity investments			(90.5	)		28.2			178.7
	Non-recurring personnel expense			(39.3	)		(23.5	)		(14.8	)
	Gains on disposal of premises and equipment			19.9			12.4			10.5
	(Provision) credit for losses on off-balance-sheet instruments			1.2			(4.6	)		(12.1	)
	Others—net			(57.8	)		(28.8	)		18.9
	Income before income tax expense			662.8			885.2			726.3

Foreign_activities_Tables

Foreign activities (Tables)	12 Months Ended
	Mar. 31, 2014
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas	'
	The following table presents consolidated income statement and total assets information by major geographic area. Foreign activities are defined as business transactions that involve customers residing outside of Japan. However, as the MHFG Group’s operations are highly integrated globally, estimates and assumptions have been made for an allocation among the geographic areas.
			Japan		Americas		Europe		Asia/Oceania		Total
									excluding
									Japan,
									and others
			(in billions of yen)
	Fiscal year ended March 31, 2012:
	Total revenue (1)			1,965.70		251.3		132		178.2		2,527.20
	Total expenses (2)			1,561.20		104		102.9		96.3		1,864.40
	Income before income tax expense			404.5		147.3		29.1		81.9		662.8
	Net income			419.2		131.2		28.1		70.5		649
	Total assets at end of fiscal year			124,443.60		25,368.90		8,868.50		7,680.60		166,361.60
	Fiscal year ended March 31, 2013:
	Total revenue (1)			2,190.70		383.7		125.8		162.6		2,862.80
	Total expenses (2)			1,668.90		140.5		48.4		119.8		1,977.60
	Income before income tax expense			521.8		243.2		77.4		42.8		885.2
	Net income			524.7		252.3		75		29.2		881.2
	Total assets at end of fiscal year			126,768.80		31,168.80		10,591.20		10,218.20		178,747.00
	Fiscal year ended March 31, 2014:
	Total revenue (1)			1,783.90		349.9		152.9		218.9		2,505.60
	Total expenses (2)			1,397.30		144.6		96.3		141.1		1,779.30
	Income before income tax expense			386.6		205.3		56.6		77.8		726.3
	Net income			198.9		189.7		54		57.6		500.2
	Total assets at end of fiscal year			124,557.70		27,527.80		10,784.50		12,829.30		175,699.30
	Notes:
	-1	Total revenue is comprised of Interest and dividend income and Noninterest income.
	-2	Total expenses are comprised of Interest expense, Provision (credit) for loan losses and Noninterest expenses.

Mizuho_Financial_Group_Inc_par1

Mizuho Financial Group, Inc., parent company (Tables)	12 Months Ended
	Mar. 31, 2014
Condensed Financial Information of Parent Company Only, Statements of Financial Condition	'
	Condensed balance sheets
		2013			2014
		(in millions of yen)
	Assets:
	Cash and due from banks		200			167
	Interest-bearing deposits in other banks		26,165			17,103
	Investments in subsidiaries and affiliated companies		6,962,630			7,501,486
	Other		152,351			210,622
	Total		7,141,346			7,729,378
	Liabilities and shareholders’ equity:
	Short-term borrowings		1,146,995			1,061,460
	Long-term debt		240,000			240,000
	Other liabilities		26,231			49,448
	Shareholders’ equity		5,728,120			6,378,470
	Total		7,141,346			7,729,378
Condensed Financial Information of Parent Company Only, Statement of Income	'
	Condensed statements of income
		2012			2013			2014
		(in millions of yen)
	Income:
	Dividends from subsidiaries and affiliated companies		7,955			233,056			285,130
	Management fees from subsidiaries		29,747			28,835			31,146
	Other income		12,643			34,668			33,894
	Total		50,345			296,559			350,170
	Expenses:
	Operating expenses		21,260			21,075			22,592
	Interest expense		16,383			15,870			14,608
	Other expense		1,431			1,207			5,724
	Total		39,074			38,152			42,924
	Equity in undistributed net income of subsidiaries		645,308			617,565			191,865
	Income before income tax expense		656,579			875,972			499,111
	Income tax expense		190			560			627
	Net income		656,389			875,412			498,484
Condensed Financial Information of Parent Company Only, Statements of Cash Flows	'
	Condensed statements of cash flows
		2012			2013			2014
		(in millions of yen)
	Cash flows from operating activities:
	Net income		656,389			875,412			498,484
	Adjustments and other		(644,977	)		(685,149	)		(222,940	)
	Net cash provided by operating activities		11,412			190,263			275,544
	Cash flows from investing activities:
	Payments for purchases of securities of subsidiaries		(212	)		—			—
	Net change in other investing activities		80			1,570			2,631
	Net cash provided by (used in) investing activities		(132	)		1,570			2,631
	Cash flows from financing activities:
	Net change in short-term borrowings		60,000			(40,000	)		(90,000	)
	Proceeds from issuance of common stock		146,499			—			—
	Purchases of treasury stock		(2,560	)		(7	)		(37,013	)
	Dividends paid		(215,937	)		(152,542	)		(152,163	)
	Net change in other financing activities		730			749			968
	Net cash used in financing activities		(11,268	)		(191,800	)		(278,208	)
	Net increase (decrease) in cash and due from banks		12			33			(33	)
	Cash and due from banks at beginning of fiscal year		155			167			200
	Cash and due from banks at end of fiscal year		167			200			167

Subsequent_events_Tables

Subsequent events (Tables)	12 Months Ended
	Mar. 31, 2014
Details of Redeemed Preferred Securities	'
	The following table describes the details of the redeemed preferred securities.
	Issuer	Aggregate		Reason for the redemption
		redemption amount
		(in millions)
	Mizuho Capital Investment (USD) 2 Limited		$850		Arrival of optional redemption date
	Mizuho Capital Investment (JPY) 5 Limited		Series A ¥139,500		Arrival of optional redemption date

Recovered_Sheet1

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Mar. 31, 2014
Minimum	'
Significant Accounting Policies [Line Items]	'
Period in which obligors generally determined to be substantially bankrupt, past due (in months)	'6 months
Minimum | Impaired loans	'
Significant Accounting Policies [Line Items]	'
Number of days past due	'90 days
Software and Software Development Costs | Minimum	'
Significant Accounting Policies [Line Items]	'
Estimated useful life	'5 years
Software and Software Development Costs | Maximum	'
Significant Accounting Policies [Line Items]	'
Estimated useful life	'10 years
Shinko Securities Company Limited | Customer relationships	'
Significant Accounting Policies [Line Items]	'
Weighted-average amortization period	'16 years

Useful_Lives_of_Premises_and_E

Useful Lives of Premises and Equipment (Detail)	12 Months Ended
	Mar. 31, 2014
Buildings | Minimum	'
Property, Plant, and Equipment Disclosure [Line Items]	'
Years	'3 years
Buildings | Maximum	'
Property, Plant, and Equipment Disclosure [Line Items]	'
Years	'50 years
Equipment and furniture | Minimum	'
Property, Plant, and Equipment Disclosure [Line Items]	'
Years	'2 years
Equipment and furniture | Maximum	'
Property, Plant, and Equipment Disclosure [Line Items]	'
Years	'20 years
Leasehold improvements | Minimum	'
Property, Plant, and Equipment Disclosure [Line Items]	'
Years	'2 years
Leasehold improvements | Maximum	'
Property, Plant, and Equipment Disclosure [Line Items]	'
Years	'50 years

Amortized_Cost_Gross_Unrealize

Amortized Cost Gross Unrealized Gains and Losses and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	¥ 28,835,446		¥ 37,825,780
Gross unrealized gains, available-for-sale securities	1,844,809		1,608,348
Gross unrealized losses, available-for-sale securities	31,494		20,177
Fair value, available-for-sale securities	30,648,761		39,413,951
Amortized cost, held-to-maturity securities	4,040,083		3,000,403
Gross unrealized gains, held-to-maturity securities	17,954		20,023
Gross unrealized losses, held-to-maturity securities	220		82
Fair value, held-to-maturity securities	4,057,817		3,020,344
Debt securities | Japanese government bonds	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	22,039,640		30,709,499
Gross unrealized gains, available-for-sale securities	20,063		79,378
Gross unrealized losses, available-for-sale securities	3,727		5,677
Fair value, available-for-sale securities	22,055,976		30,783,200
Amortized cost, held-to-maturity securities	4,040,083		3,000,403
Gross unrealized gains, held-to-maturity securities	17,954		20,023
Gross unrealized losses, held-to-maturity securities	220		82
Fair value, held-to-maturity securities	4,057,817		3,020,344
Debt securities | Japanese corporate bonds and other debt securities	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	2,015,045		2,197,270
Gross unrealized gains, available-for-sale securities	16,316		22,582
Gross unrealized losses, available-for-sale securities	3,284		5,288
Fair value, available-for-sale securities	2,028,077	[1]	2,214,564	[1]
Debt securities | Japanese local government bonds	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	241,985		239,695
Gross unrealized gains, available-for-sale securities	2,783		4,109
Gross unrealized losses, available-for-sale securities	106		47
Fair value, available-for-sale securities	244,662		243,757
Debt securities | U.S. Treasury bonds and federal agency securities	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	158,344		177,438
Gross unrealized gains, available-for-sale securities	434		623
Gross unrealized losses, available-for-sale securities	4,297		36
Fair value, available-for-sale securities	154,481		178,025
Debt securities | Foreign corporate bonds and other debt securities	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	559,947		542,958
Gross unrealized gains, available-for-sale securities	10,755		17,768
Gross unrealized losses, available-for-sale securities	2,193		1,803
Fair value, available-for-sale securities	568,509	[2]	558,923	[2]
Debt securities | Agency mortgage-backed securities	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	955,291		986,646
Gross unrealized gains, available-for-sale securities	13,288		20,496
Gross unrealized losses, available-for-sale securities	7,705		1,429
Fair value, available-for-sale securities	960,874	[3]	1,005,713	[3]
Debt securities | Residential mortgage-backed securities	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	318,955		430,325
Gross unrealized gains, available-for-sale securities	14,757		13,889
Gross unrealized losses, available-for-sale securities	1,707		2,131
Fair value, available-for-sale securities	332,005		442,083
Debt securities | Commercial mortgage-backed securities	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	159,289		246,169
Gross unrealized gains, available-for-sale securities	3,032		7,487
Gross unrealized losses, available-for-sale securities	1,417		3,528
Fair value, available-for-sale securities	160,904		250,128
Debt securities | Other foreign government bonds	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	719,281		596,305
Gross unrealized gains, available-for-sale securities	2,356		1,914
Gross unrealized losses, available-for-sale securities	455		94
Fair value, available-for-sale securities	721,182		598,125
Equity securities (marketable)	'		'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'		'
Amortized cost, available-for-sale securities	1,667,669		1,699,475
Gross unrealized gains, available-for-sale securities	1,761,025		1,440,102
Gross unrealized losses, available-for-sale securities	6,603		144
Fair value, available-for-sale securities	¥ 3,422,091		¥ 3,139,433
[1]	Other debt securities presented in the above table primarily consist of certificates of deposit ("CDs") and asset-backed securities ("ABS"), of which the total fair values were ¥185,497 million at March 31,2013, and ¥214,488 million at March 31, 2014.
[2]	Other debt securities presented in the above table primarily consist of CDs, ABS, and collateral loan obligations ("CLO"), of which the total fair values were ¥243,633 million at March 31,2013, and ¥178,055 million at March 31, 2014.
[3]	Agency mortgage-backed securities presented in the above table consist of U.S. agency securities and Japanese agency securities, of which the fair values were ¥143,954 million and ¥861,759 million, respectively, at March 31, 2013, and ¥105,553 million and ¥855,321 million, respectively, at March 31, 2014. U.S. agency securities primarily consist of Government National Mortgage Association or Ginnie Mae securities, which are guaranteed by the United States government. All Japanese agency securities are mortgage-backed securities issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise.

Amortized_Cost_Gross_Unrealize1

Amortized Cost Gross Unrealized Gains and Losses and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Parenthetical) (Detail)

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

In Millions, unless otherwise specified

JPY (¥)

JPY (¥)

Debt securities

Debt securities

Debt securities

Debt securities

Debt securities

Debt securities

Other debt securities

Other debt securities

Other debt securities

Other debt securities

Agency mortgage-backed securities

Agency mortgage-backed securities

Agency mortgage-backed securities

Agency mortgage-backed securities

Agency mortgage-backed securities

Agency mortgage-backed securities

Certificates of deposit ("CDs") and Asset-Backed Securities ("ABS")

Certificates of deposit ("CDs") and Asset-Backed Securities ("ABS")

CDs, ABS, and collateral loan obligations ("CLO")

CDs, ABS, and collateral loan obligations ("CLO")

JPY (¥)

JPY (¥)

U.S. agency securities

U.S. agency securities

Japanese agency securities

Japanese agency securities

USD ($)

USD ($)

JPY (¥)

JPY (¥)

JPY (¥)

JPY (¥)

JPY (¥)

JPY (¥)

Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Fair value, available-for-sale securities

¥ 30,648,761

¥ 39,413,951

¥ 960,874

[1]

¥ 1,005,713

[1]

¥ 105,553

¥ 143,954

¥ 855,321

¥ 861,759

$214,488

$185,497

¥ 178,055

¥ 243,633

[1]

Agency mortgage-backed securities presented in the above table consist of U.S. agency securities and Japanese agency securities, of which the fair values were ¥143,954 million and ¥861,759 million, respectively, at March 31, 2013, and ¥105,553 million and ¥855,321 million, respectively, at March 31, 2014. U.S. agency securities primarily consist of Government National Mortgage Association or Ginnie Mae securities, which are guaranteed by the United States government. All Japanese agency securities are mortgage-backed securities issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise.

Amortized_Cost_and_Fair_Value_

Amortized Cost and Fair Value of Available-for-sale and Held-to-maturity Debt Securities by Contractual Maturity (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, unless otherwise specified
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due in one year or less, amortized cost	¥ 7,102,998	'
Due after one year through five years, amortized cost	15,800,383	'
Due after five years through ten years,amortized cost	2,799,710	'
Due after ten years, amortized cost	1,464,686	'
Total	27,167,777	'
Due in one year or less, amortized cost	600,047	'
Due after one year through five years, amortized cost	3,080,346	'
Due after five years through ten years, amortized cost	359,690	'
Due after ten years, amortized cost	'	'
Total	4,040,083	3,000,403
Due in one year or less, fair value	7,105,281	'
Due after one year through five years, fair value	15,814,574	'
Due after five years through ten years, fair value	2,817,841	'
Due after ten years, fair value	1,488,974	'
Total	27,226,670	'
Due in one year or less, fair value	601,750	'
Due after one year through five years, fair value	3,091,769	'
Due after five years through ten years, fair value	364,298	'
Due after ten years, fair value	'	'
Fair value, held-to-maturity securities	4,057,817	3,020,344
Debt securities | Japanese government bonds	'	'
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due in one year or less, amortized cost	5,926,354	'
Due after one year through five years, amortized cost	13,876,023	'
Due after five years through ten years,amortized cost	2,237,263	'
Total	22,039,640	'
Due in one year or less, amortized cost	600,047	'
Due after one year through five years, amortized cost	3,080,346	'
Due after five years through ten years, amortized cost	359,690	'
Due after ten years, amortized cost	'	'
Total	4,040,083	3,000,403
Due in one year or less, fair value	5,926,642	'
Due after one year through five years, fair value	13,882,371	'
Due after five years through ten years, fair value	2,246,963	'
Total	22,055,976	'
Due in one year or less, fair value	601,750	'
Due after one year through five years, fair value	3,091,769	'
Due after five years through ten years, fair value	364,298	'
Due after ten years, fair value	'	'
Fair value, held-to-maturity securities	4,057,817	3,020,344
Debt securities | Japanese local government bonds	'	'
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due in one year or less, amortized cost	30,346	'
Due after one year through five years, amortized cost	130,751	'
Due after five years through ten years,amortized cost	80,108	'
Due after ten years, amortized cost	780	'
Total	241,985	'
Due in one year or less, fair value	30,384	'
Due after one year through five years, fair value	131,438	'
Due after five years through ten years, fair value	81,952	'
Due after ten years, fair value	888	'
Total	244,662	'
Debt securities | U.S. Treasury bonds and federal agency securities	'	'
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due in one year or less, amortized cost	43,475	'
Due after one year through five years, amortized cost	75,005	'
Due after five years through ten years,amortized cost	39,864	'
Total	158,344	'
Due in one year or less, fair value	43,907	'
Due after one year through five years, fair value	72,142	'
Due after five years through ten years, fair value	38,432	'
Total	154,481	'
Debt securities | Other foreign government bonds	'	'
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due in one year or less, amortized cost	507,140	'
Due after one year through five years, amortized cost	211,949	'
Due after ten years, amortized cost	192	'
Total	719,281	'
Due in one year or less, fair value	507,577	'
Due after one year through five years, fair value	213,355	'
Due after ten years, fair value	250	'
Total	721,182	'
Debt securities | Agency mortgage-backed securities	'	'
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due after ten years, amortized cost	955,291	'
Total	955,291	'
Due after ten years, fair value	960,874	'
Total	960,874	'
Debt securities | Residential mortgage-backed securities	'	'
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due after ten years, amortized cost	318,955	'
Total	318,955	'
Due after ten years, fair value	332,005	'
Total	332,005	'
Debt securities | Commercial mortgage-backed securities	'	'
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due in one year or less, amortized cost	4,085	'
Due after one year through five years, amortized cost	123,455	'
Due after five years through ten years,amortized cost	31,749	'
Total	159,289	'
Due in one year or less, fair value	4,087	'
Due after one year through five years, fair value	124,981	'
Due after five years through ten years, fair value	31,836	'
Total	160,904	'
Debt securities | Japanese corporate bonds and other debt securities	'	'
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due in one year or less, amortized cost	369,682	'
Due after one year through five years, amortized cost	1,131,664	'
Due after five years through ten years,amortized cost	326,861	'
Due after ten years, amortized cost	186,838	'
Total	2,015,045	'
Due in one year or less, fair value	370,157	'
Due after one year through five years, fair value	1,137,145	'
Due after five years through ten years, fair value	329,033	'
Due after ten years, fair value	191,742	'
Total	2,028,077	'
Debt securities | Foreign corporate bonds and other debt securities	'	'
Investments Classified by Contractual Maturity Date [Line Items]	'	'
Due in one year or less, amortized cost	221,916	'
Due after one year through five years, amortized cost	251,536	'
Due after five years through ten years,amortized cost	83,865	'
Due after ten years, amortized cost	2,630	'
Total	559,947	'
Due in one year or less, fair value	222,527	'
Due after one year through five years, fair value	253,142	'
Due after five years through ten years, fair value	89,625	'
Due after ten years, fair value	3,215	'
Total	¥ 568,509	'

Investments_Additional_Informa

Investments - Additional Information (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Gain (Loss) on Investments [Line Items]	'	'	'
Available-for-sale securities, gross realized gains on sales	¥ 231,955	¥ 193,298	¥ 100,371
Available-for-sale securities, gross realized losses on sales	29,387	21,422	28,840
Equity method Investments, carrying value	196,015	225,696	'
Equity method investments, earnings (losses)	27,975	-2,192	10,807
Available-for-sale securities	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount	5,344	76,393	117,029
Available-for-sale securities | Debt securities	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount	1,151	4,085	7,238
Available-for-sale securities | Equity securities	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount	4,193	72,308	109,791
Orico	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Percentage of proportionate share to the total outstanding common shares	22.20%	'	'
Maximum percentage of proportionate share to the total outstanding common shares if convertible preferred shares are fully converted	58.00%	'	'
Equity securities (marketable)	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Equity method Investments, carrying value	78,458	68,289	'
Equity method Investments, aggregated market values	¥ 96,471	¥ 111,543	'

Gross_Unrealized_Losses_and_Fa

Gross Unrealized Losses and Fair Value of Available-for-Sale and Held-to-Maturity Securities Aggregated by Length of Time that Individual Securities have been in Continuous Unrealized Loss Position (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	¥ 11,353,525		¥ 5,625,850
Less than 12 months Gross unrealized losses, available-for-sale securities	17,511		3,821
12 months or more Fair value, available-for-sale securities	1,232,013		940,267
12 months or more Gross unrealized losses, available-for-sale securities	13,983		16,356
Total Fair value, available-for-sale securities	12,585,538		6,566,117
Total Gross unrealized losses, available-for-sale securities	31,494		20,177
Less than 12 months, Fair value, held-to-maturity securities	9,962		199,730
Less than 12 months Gross unrealized losses, held-to-maturity securities	40		82
12 months or more Fair value, held-to-maturity securities	199,670		'
12 months or more Gross unrealized losses, held-to-maturity securities	180		'
Total Fair value, held-to-maturity securities	209,632		199,730
Total Gross unrealized losses, held-to-maturity securities	220		82
Debt securities | Agency mortgage-backed securities	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	102,904		90,832
Less than 12 months Gross unrealized losses, available-for-sale securities	2,348		1,429
12 months or more Fair value, available-for-sale securities	76,369		'
12 months or more Gross unrealized losses, available-for-sale securities	5,357		'
Total Fair value, available-for-sale securities	179,273	[1]	90,832	[2]
Total Gross unrealized losses, available-for-sale securities	7,705		1,429
Debt securities | Japanese government bonds	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	10,526,182		5,059,495
Less than 12 months Gross unrealized losses, available-for-sale securities	2,871		1,520
12 months or more Fair value, available-for-sale securities	880,520		406,684
12 months or more Gross unrealized losses, available-for-sale securities	856		4,157
Total Fair value, available-for-sale securities	11,406,702		5,466,179
Total Gross unrealized losses, available-for-sale securities	3,727		5,677
Less than 12 months, Fair value, held-to-maturity securities	9,962		199,730
Less than 12 months Gross unrealized losses, held-to-maturity securities	40		82
12 months or more Fair value, held-to-maturity securities	199,670		'
12 months or more Gross unrealized losses, held-to-maturity securities	180		'
Total Fair value, held-to-maturity securities	209,632		199,730
Total Gross unrealized losses, held-to-maturity securities	220		82
Debt securities | Japanese local government bonds	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	48,471		27,243
Less than 12 months Gross unrealized losses, available-for-sale securities	90		47
12 months or more Fair value, available-for-sale securities	12,730		'
12 months or more Gross unrealized losses, available-for-sale securities	16		'
Total Fair value, available-for-sale securities	61,201		27,243
Total Gross unrealized losses, available-for-sale securities	106		47
Debt securities | U.S. Treasury bonds and federal agency securities	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	66,865		69,168
Less than 12 months Gross unrealized losses, available-for-sale securities	2,865		36
12 months or more Fair value, available-for-sale securities	38,432		'
12 months or more Gross unrealized losses, available-for-sale securities	1,432		'
Total Fair value, available-for-sale securities	105,297		69,168
Total Gross unrealized losses, available-for-sale securities	4,297		36
Debt securities | Other foreign government bonds	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	203,026		207,942
Less than 12 months Gross unrealized losses, available-for-sale securities	275		94
12 months or more Fair value, available-for-sale securities	7,654		'
12 months or more Gross unrealized losses, available-for-sale securities	180		'
Total Fair value, available-for-sale securities	210,680		207,942
Total Gross unrealized losses, available-for-sale securities	455		94
Debt securities | Residential mortgage-backed securities	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	9,771		12,778
Less than 12 months Gross unrealized losses, available-for-sale securities	137		9
12 months or more Fair value, available-for-sale securities	78,938		122,363
12 months or more Gross unrealized losses, available-for-sale securities	1,570		2,122
Total Fair value, available-for-sale securities	88,709		135,141
Total Gross unrealized losses, available-for-sale securities	1,707		2,131
Debt securities | Commercial mortgage-backed securities	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	11,133		7,159
Less than 12 months Gross unrealized losses, available-for-sale securities	117		111
12 months or more Fair value, available-for-sale securities	43,170		122,588
12 months or more Gross unrealized losses, available-for-sale securities	1,300		3,417
Total Fair value, available-for-sale securities	54,303		129,747
Total Gross unrealized losses, available-for-sale securities	1,417		3,528
Debt securities | Japanese corporate bonds and other debt securities	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	130,020		88,146
Less than 12 months Gross unrealized losses, available-for-sale securities	359		333
12 months or more Fair value, available-for-sale securities	60,230		222,516
12 months or more Gross unrealized losses, available-for-sale securities	2,925		4,955
Total Fair value, available-for-sale securities	190,250		310,662
Total Gross unrealized losses, available-for-sale securities	3,284		5,288
Debt securities | Foreign corporate bonds and other debt securities	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	122,563		54,599
Less than 12 months Gross unrealized losses, available-for-sale securities	1,846		114
12 months or more Fair value, available-for-sale securities	33,960		65,417
12 months or more Gross unrealized losses, available-for-sale securities	347		1,689
Total Fair value, available-for-sale securities	156,523		120,016
Total Gross unrealized losses, available-for-sale securities	2,193		1,803
Equity securities (marketable)	'		'
Gain (Loss) on Investments [Line Items]	'		'
Less than 12 months, Fair value, available-for-sale securities	132,590		8,488
Less than 12 months Gross unrealized losses, available-for-sale securities	6,603		128
12 months or more Fair value, available-for-sale securities	10		699
12 months or more Gross unrealized losses, available-for-sale securities	'		16
Total Fair value, available-for-sale securities	132,600		9,187
Total Gross unrealized losses, available-for-sale securities	¥ 6,603		¥ 144
[1]	Agency mortgage-backed securities presented in the above table consist of U.S. agency securities and Japanese agency securities, of which the fair values were ¥105,208 million and ¥74,065 million, respectively, at March 31, 2014. All Japanese agency securities are mortgage-backed securities issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise.
[2]	Agency mortgage-backed securities presented in the above table represent U.S. agency securities. U.S. agency securities primarily consist of Government National Mortgage Association or Ginnie Mae securities, which are guaranteed by the United States government.

Gross_Unrealized_Losses_and_Fa1

Gross Unrealized Losses and Fair Value of Available-for-Sale and Held-to-Maturity Securities Aggregated by Length of Time that Individual Securities have been in Continuous Unrealized Loss Position (Parenthetical) (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Gain (Loss) on Investments [Line Items]	'		'
Fair value, available-for-sale securities	¥ 12,585,538		¥ 6,566,117
Debt securities | Agency mortgage-backed securities	'		'
Gain (Loss) on Investments [Line Items]	'		'
Fair value, available-for-sale securities	179,273	[1]	90,832	[2]
Debt securities | Agency mortgage-backed securities | U.S. agency securities	'		'
Gain (Loss) on Investments [Line Items]	'		'
Fair value, available-for-sale securities	105,208		'
Debt securities | Agency mortgage-backed securities | Japanese agency securities	'		'
Gain (Loss) on Investments [Line Items]	'		'
Fair value, available-for-sale securities	¥ 74,065		'
[1]	Agency mortgage-backed securities presented in the above table consist of U.S. agency securities and Japanese agency securities, of which the fair values were ¥105,208 million and ¥74,065 million, respectively, at March 31, 2014. All Japanese agency securities are mortgage-backed securities issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise.
[2]	Agency mortgage-backed securities presented in the above table represent U.S. agency securities. U.S. agency securities primarily consist of Government National Mortgage Association or Ginnie Mae securities, which are guaranteed by the United States government.

Composition_of_Other_Investmen

Composition of Other Investments (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, unless otherwise specified
Schedule of Cost-method Investments [Line Items]	'	'
Equity method investments	¥ 196,015	¥ 225,696
Investments held by consolidated investment companies	70,599	75,780
Other equity interests	526,075	536,659
Total	¥ 792,689	¥ 838,135

Loans_Outstanding_by_Domicile_

Loans Outstanding by Domicile and Industry of Borrower (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	¥ 73,623,540	[1]	¥ 69,945,464	[1]
Less: Unearned income and deferred loan fees-net	138,586		111,981
Loans outstanding	73,484,954		69,833,483
Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	54,938,307		54,580,313
Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	8,025,932		8,078,871
Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	7,204,594		7,477,853
Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,956,742		3,972,011
Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	5,350,707		5,355,974
Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,247,394		3,147,106
Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,460,147		3,142,998
Domestic | Government and public institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	6,734,451		6,907,426
Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	4,983,821	[2]	4,521,994	[2]
Domestic | Mortgage loans	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	11,187,206		11,234,561
Domestic | Other individual loans	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	787,313		741,519
Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	18,685,233		15,365,151
Foreign | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	4,610,141		4,088,651
Foreign | Government and public institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	883,004		595,911
Foreign | Commercial and industrial	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	12,937,005		10,481,071
Foreign | Other	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	¥ 255,083	[2]	¥ 199,518	[2]
[1]	Amounts represent loan balances before deducting unearned income and deferred loan fees.
[2]	Other industries of domestic and Other of foreign include trade receivables and lease receivables of consolidated VIEs.

Loans_Additional_Information_D

Loans - Additional Information (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Net losses on sales of loans	¥ 2,041	¥ 853	¥ 4,576
Impaired Financing Receivables with No Related Allowance	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Impaired loans partially charged off	24,957	51,720	'
Valuation losses related to loans held for sale accounted for at the lower of cost or fair value	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Net losses on sales of loans, amount attributable to valuation losses related to loans held for sale accounted for at the lower of cost or fair value	¥ 1,510	¥ 54	¥ 3,435

Credit_Quality_Indicators_of_F

Credit Quality Indicators of Financing Receivables (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	¥ 73,623,540	[1]	¥ 69,945,464	[1]
Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	54,938,307		54,580,313
Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	8,025,932		8,078,871
Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	7,204,594		7,477,853
Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,956,742		3,972,011
Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	5,350,707		5,355,974
Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,247,394		3,147,106
Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,460,147		3,142,998
Domestic | Government and public institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	6,734,451		6,907,426
Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	4,983,821	[2]	4,521,994	[2]
Domestic | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	11,974,519		11,976,080
Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	18,685,233		15,365,151
Foreign | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	4,610,141		4,088,651
Foreign | Government and public institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	883,004		595,911
Financing Receivables Not Impaired | Normal obligors | A-B	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	35,292,975		31,480,416
Financing Receivables Not Impaired | Normal obligors | A-B | Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	24,692,444		23,186,762
Financing Receivables Not Impaired | Normal obligors | A-B | Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	4,248,490		4,171,212
Financing Receivables Not Impaired | Normal obligors | A-B | Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,890,563		2,524,644
Financing Receivables Not Impaired | Normal obligors | A-B | Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	1,946,764		1,736,931
Financing Receivables Not Impaired | Normal obligors | A-B | Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,029,723		1,853,573
Financing Receivables Not Impaired | Normal obligors | A-B | Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,388,541		2,236,404
Financing Receivables Not Impaired | Normal obligors | A-B | Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,602,545		2,246,804
Financing Receivables Not Impaired | Normal obligors | A-B | Domestic | Government and public institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	6,678,104		6,797,133
Financing Receivables Not Impaired | Normal obligors | A-B | Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	1,907,714		1,620,061
Financing Receivables Not Impaired | Normal obligors | A-B | Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	10,600,531		8,293,654
Financing Receivables Not Impaired | Normal obligors | C-D	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	16,358,154		16,484,016
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	12,008,567		12,833,528
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,467,326		2,615,406
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,066,852		3,486,850
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	1,558,609		1,734,482
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,632,048		2,699,053
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	658,680		685,237
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	664,843		666,197
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic | Government and public institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	8,347		11,729
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	754,137		743,214
Financing Receivables Not Impaired | Normal obligors | C-D | Domestic | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	197,725		191,360
Financing Receivables Not Impaired | Normal obligors | C-D | Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	4,349,587		3,650,488
Financing Receivables Not Impaired | Normal obligors | Retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	12,555,451	[3]	12,583,274	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	12,548,830	[3]	12,578,393	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	109,258	[3]	119,183	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	623,385	[3]	659,844	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	205,939	[3]	219,089	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	249,304	[3]	261,322	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	88,911	[3]	94,233	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,030	[3]	2,172	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,383	[3]	3,341	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Domestic | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	11,266,620	[3]	11,219,209	[3]
Financing Receivables Not Impaired | Normal obligors | Retail | Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	6,621	[3]	4,881	[3]
Financing Receivables Not Impaired | Normal obligors | Other	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	5,789,132	[4]	4,899,190	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,006,656	[4]	2,877,906	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	310,703	[4]	307,946	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	161,177	[4]	148,893	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	6,998	[4]	4,035	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	63,116	[4]	83,065	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	1,348	[4]	350	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	4,780	[4]	5,311	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic | Government and public institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	48,000	[4]	98,564	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,240,879	[4]	2,058,974	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Domestic | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	169,655	[4]	170,768	[4]
Financing Receivables Not Impaired | Normal obligors | Other | Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,782,476	[4]	2,021,284	[4]
Financing Receivables Not Impaired | Watch obligors | Retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	222,195	[3],[5]	254,119	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	222,181	[3],[5]	253,982	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	21,117	[3],[5]	22,569	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	20,577	[3],[5]	20,671	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	24,958	[3],[5]	26,621	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	42,086	[3],[5]	49,710	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	11,159	[3],[5]	12,274	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	165	[3],[5]	221	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	401	[3],[5]	448	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Domestic | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	101,718	[3],[5]	121,468	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Retail | Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	14	[3],[5]	137	[3],[5]
Financing Receivables Not Impaired | Watch obligors | Other	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	219,914	[4],[5]	201,952	[4],[5]
Financing Receivables Not Impaired | Watch obligors | Other | Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	75,676	[4],[5]	90,268	[4],[5]
Financing Receivables Not Impaired | Watch obligors | Other | Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	3,820	[4],[5]	8,013	[4],[5]
Financing Receivables Not Impaired | Watch obligors | Other | Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	381	[4],[5]	664	[4],[5]
Financing Receivables Not Impaired | Watch obligors | Other | Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	10	[4],[5]	11	[4],[5]
Financing Receivables Not Impaired | Watch obligors | Other | Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	68,642	[4],[5]	77,548	[4],[5]
Financing Receivables Not Impaired | Watch obligors | Other | Domestic | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,823	[4],[5]	4,032	[4],[5]
Financing Receivables Not Impaired | Watch obligors | Other | Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	144,238	[4],[5]	111,684	[4],[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	2,040,659	[5]	2,578,279	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	1,527,049	[5]	1,597,936	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	636,348	[5]	498,638	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	303,746	[5]	387,254	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	135,030	[5]	160,754	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	178,520	[5]	236,545	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	50,667	[5]	59,573	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	174,328	[5]	208,510	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	7,804	[5]	13,044	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Domestic | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	40,606	[5]	33,618	[5]
Financing Receivables Not Impaired | Watch obligors | E1 to E2 Rating | Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	513,610	[5]	980,343	[5]
Financing Receivables Impaired | Impaired loans	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	1,145,060		1,464,218
Financing Receivables Impaired | Impaired loans | Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	856,904		1,161,538
Financing Receivables Impaired | Impaired loans | Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	228,870		335,904
Financing Receivables Impaired | Impaired loans | Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	137,913		249,033
Financing Receivables Impaired | Impaired loans | Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	78,444		90,099
Financing Receivables Impaired | Impaired loans | Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	155,900		172,695
Financing Receivables Impaired | Impaired loans | Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	48,088		59,035
Financing Receivables Impaired | Impaired loans | Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	11,456		13,783
Financing Receivables Impaired | Impaired loans | Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	861		5,364
Financing Receivables Impaired | Impaired loans | Domestic | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	195,372		235,625
Financing Receivables Impaired | Impaired loans | Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Loans outstanding	¥ 288,156		¥ 302,680
[1]	Amounts represent loan balances before deducting unearned income and deferred loan fees.
[2]	Other industries of domestic and Other of foreign include trade receivables and lease receivables of consolidated VIEs.
[3]	Amounts represent small balance, homogeneous loans which are subject to pool allocations.
[4]	The former MHBK and the former Mizuho Corporate Bank, Ltd. ("MHCB") merged on July 1, 2013 and the former MHCB, the surviving company, changed its trade name to MHBK. As of March 31, 2013, non-impaired loans held by subsidiaries other than the former MHBK, the former MHCB and MHTB constitute Other, since their portfolio segments are not identical to those used by the former MHBK, the former MHCB and MHTB. As of March 31, 2014, non-impaired loans held by subsidiaries other than MHBK and MHTB constitute Other, since their portfolio segments are not identical to those used by MHBK and MHTB.
[5]	Special attention obligors are watch obligors with debt in TDR or 90 days or more delinquent debt. Loans to such obligors are considered impaired.

Impaired_Loans_Detail

Impaired Loans (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	¥ 958,463	[1]	¥ 1,242,133	[1]
Recorded investment not requiring an allowance for loan losses	186,597	[1],[2]	222,085	[1],[2]
Total	1,145,060	[1]	1,464,218	[1]
Unpaid principal balance	1,229,802		1,569,289
Related allowance	323,163	[3]	406,341	[3]
Average recorded investment	1,262,118		1,360,258
Interest income recognized	20,350	[4]	24,330	[4]
Domestic Country	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	682,171	[1]	944,274	[1]
Recorded investment not requiring an allowance for loan losses	174,733	[1],[2]	217,264	[1],[2]
Total	856,904	[1]	1,161,538	[1]
Unpaid principal balance	939,641		1,263,488
Related allowance	204,803	[3]	287,288	[3]
Average recorded investment	970,137		1,139,697
Interest income recognized	15,600	[4]	19,009	[4]
Domestic Country | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	216,579	[1]	325,727	[1]
Recorded investment not requiring an allowance for loan losses	12,291	[1],[2]	10,177	[1],[2]
Total	228,870	[1]	335,904	[1]
Unpaid principal balance	240,660		365,049
Related allowance	74,367	[3]	118,475	[3]
Average recorded investment	259,889		299,978
Interest income recognized	4,086	[4]	5,297	[4]
Domestic Country | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	107,932	[1]	189,060	[1]
Recorded investment not requiring an allowance for loan losses	29,981	[1],[2]	59,973	[1],[2]
Total	137,913	[1]	249,033	[1]
Unpaid principal balance	163,813		269,770
Related allowance	30,724	[3]	46,574	[3]
Average recorded investment	183,437		227,920
Interest income recognized	2,213	[4]	2,824	[4]
Domestic Country | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	66,651	[1]	77,982	[1]
Recorded investment not requiring an allowance for loan losses	11,793	[1],[2]	12,117	[1],[2]
Total	78,444	[1]	90,099	[1]
Unpaid principal balance	88,537		106,397
Related allowance	20,199	[3]	22,153	[3]
Average recorded investment	83,754		103,113
Interest income recognized	1,671	[4]	1,949	[4]
Domestic Country | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	142,886	[1]	160,477	[1]
Recorded investment not requiring an allowance for loan losses	13,014	[1],[2]	12,218	[1],[2]
Total	155,900	[1]	172,695	[1]
Unpaid principal balance	172,641		189,231
Related allowance	51,274	[3]	62,962	[3]
Average recorded investment	161,288		186,594
Interest income recognized	2,795	[4]	3,076	[4]
Domestic Country | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	44,237	[1]	55,202	[1]
Recorded investment not requiring an allowance for loan losses	3,851	[1],[2]	3,833	[1],[2]
Total	48,088	[1]	59,035	[1]
Unpaid principal balance	54,149		61,554
Related allowance	14,691	[3]	18,870	[3]
Average recorded investment	50,387		54,633
Interest income recognized	939	[4]	1,220	[4]
Domestic Country | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	11,390	[1]	13,727	[1]
Recorded investment not requiring an allowance for loan losses	66	[1],[2]	56	[1],[2]
Total	11,456	[1]	13,783	[1]
Unpaid principal balance	11,480		13,821
Related allowance	4,049	[3]	5,007	[3]
Average recorded investment	12,474		11,950
Interest income recognized	163	[4]	227	[4]
Domestic Country | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	781	[1]	5,224	[1]
Recorded investment not requiring an allowance for loan losses	80	[1],[2]	140	[1],[2]
Total	861	[1]	5,364	[1]
Unpaid principal balance	2,020		5,484
Related allowance	108	[3]	3,818	[3]
Average recorded investment	3,486		4,791
Interest income recognized	19	[4]	73	[4]
Domestic Country | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	91,715	[1]	116,875	[1]
Recorded investment not requiring an allowance for loan losses	103,657	[1],[2]	118,750	[1],[2]
Total	195,372	[1]	235,625	[1]
Unpaid principal balance	206,341		252,182
Related allowance	9,391	[3]	9,429	[3]
Average recorded investment	215,422		250,718
Interest income recognized	3,714	[4]	4,343	[4]
Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment requiring an allowance for loan losses	276,292	[1]	297,859	[1]
Recorded investment not requiring an allowance for loan losses	11,864	[1],[2]	4,821	[1],[2]
Total	288,156	[1]	302,680	[1]
Unpaid principal balance	290,161		305,801
Related allowance	118,360	[3]	119,053	[3]
Average recorded investment	291,981		220,561
Interest income recognized	¥ 4,750	[4]	¥ 5,321	[4]
[1]	Amounts represent the outstanding balances of nonaccrual loans. The MHFG Group's policy for placing loans in nonaccrual status completely corresponds to the Group's definition of impaired loans.
[2]	These impaired loans do not require an allowance for loan losses because the MHFG Group has sufficient collateral to cover probable loan losses.
[3]	The allowance for loan losses on impaired loans includes those for groups of small balance, homogeneous loans totaling ¥504,750 million and ¥425,391 million as of March 31, 2013 and 2014 which were collectively evaluated for impairment, in addition to those that were individually evaluated for impairment.
[4]	Amounts represent gross interest income on impaired loans which were included in Interest income on loans in the consolidated statements of income.

Impaired_Loans_Parenthetical_D

Impaired Loans (Parenthetical) (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment	¥ 1,145,060	[1]	¥ 1,464,218	[1]
Small balance homogeneous loans of which were collectively evaluated for impairment	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Recorded investment	¥ 425,391		¥ 504,750
[1]	Amounts represent the outstanding balances of nonaccrual loans. The MHFG Group's policy for placing loans in nonaccrual status completely corresponds to the Group's definition of impaired loans.

Troubled_Debt_Restructuring_De

Troubled Debt Restructuring (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Financing Receivable, Modifications [Line Items]	'		'
Loan forgiveness or debt to equity swaps Recorded investment	¥ 3,078	[1]	¥ 1,062	[1]
Loan forgiveness or debt to equity swaps charge-off	1,321	[2]	4,993	[2]
Interest rate reduction and/or Postponement of principal and/or interest	646,107		985,999
Domestic	'		'
Financing Receivable, Modifications [Line Items]	'		'
Loan forgiveness or debt to equity swaps Recorded investment	3,078	[1]	'
Loan forgiveness or debt to equity swaps charge-off	1,321	[2]	1,243	[2]
Interest rate reduction and/or Postponement of principal and/or interest	585,759		845,935
Domestic | Manufacturing	'		'
Financing Receivable, Modifications [Line Items]	'		'
Loan forgiveness or debt to equity swaps Recorded investment	235	[1]	'
Loan forgiveness or debt to equity swaps charge-off	481	[2]	'
Interest rate reduction and/or Postponement of principal and/or interest	196,705		277,957
Domestic | Construction and real estate	'		'
Financing Receivable, Modifications [Line Items]	'		'
Loan forgiveness or debt to equity swaps Recorded investment	2,528	[1]	'
Loan forgiveness or debt to equity swaps charge-off	136	[2]	'
Interest rate reduction and/or Postponement of principal and/or interest	44,573		129,908
Domestic | Services	'		'
Financing Receivable, Modifications [Line Items]	'		'
Loan forgiveness or debt to equity swaps Recorded investment	310	[1]	'
Loan forgiveness or debt to equity swaps charge-off	555	[2]	'
Interest rate reduction and/or Postponement of principal and/or interest	57,945		68,930
Domestic | Wholesale and retail	'		'
Financing Receivable, Modifications [Line Items]	'		'
Loan forgiveness or debt to equity swaps Recorded investment	5	[1]	'
Loan forgiveness or debt to equity swaps charge-off	149	[2]	1,243	[2]
Interest rate reduction and/or Postponement of principal and/or interest	170,217		218,497
Domestic | Transportation and communications	'		'
Financing Receivable, Modifications [Line Items]	'		'
Interest rate reduction and/or Postponement of principal and/or interest	34,598		52,206
Domestic | Banks and other financial institutions	'		'
Financing Receivable, Modifications [Line Items]	'		'
Interest rate reduction and/or Postponement of principal and/or interest	31,901		34,468
Domestic | Other industries	'		'
Financing Receivable, Modifications [Line Items]	'		'
Interest rate reduction and/or Postponement of principal and/or interest	1,998		1,809
Domestic | Individuals	'		'
Financing Receivable, Modifications [Line Items]	'		'
Interest rate reduction and/or Postponement of principal and/or interest	47,822		62,160
Foreign	'		'
Financing Receivable, Modifications [Line Items]	'		'
Loan forgiveness or debt to equity swaps Recorded investment	'		1,062	[1]
Loan forgiveness or debt to equity swaps charge-off	'		3,750	[2]
Interest rate reduction and/or Postponement of principal and/or interest	¥ 60,348		¥ 140,064
[1]	Amounts represent the book values of loans immediately after the restructurings.
[2]	Charge-offs represent the loss impact on the consolidated statements of income for the fiscal year that resulted from the restructurings.

Loans_Modified_as_Troubled_Deb

Loans Modified as Troubled Debt Restructuring within Previous Twelve Months and for which There Was Payment Default During Current Fiscal Year (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	¥ 70,841	¥ 79,664
Domestic	'	'
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	70,726	73,290
Domestic | Manufacturing	'	'
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	21,144	18,740
Domestic | Construction and real estate	'	'
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	3,500	18,751
Domestic | Services	'	'
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	3,707	5,976
Domestic | Wholesale and retail	'	'
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	21,916	19,920
Domestic | Transportation and communications	'	'
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	14,069	4,386
Domestic | Other industries	'	'
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	107	'
Domestic | Individuals	'	'
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	6,283	5,517
Foreign	'	'
Financing Receivable, Modifications [Line Items]	'	'
Recorded investment	¥ 115	¥ 6,374

Analysis_Age_of_Recorded_Inves

Analysis Age of Recorded Investment in Financing Receivables that Past Due (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	¥ 53,030		¥ 64,584
60-89 days past due	30,543		36,291
90 days or more past due	152,632		217,196
Total past due	236,205		318,071
Current	73,387,335		69,627,393
Total	73,623,540	[1]	69,945,464	[1]
Domestic	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	52,943		64,457
60-89 days past due	30,520		35,406
90 days or more past due	141,697		206,064
Total past due	225,160		305,927
Current	54,713,147		54,274,386
Total	54,938,307		54,580,313
Domestic | Manufacturing	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	2,834		3,788
60-89 days past due	2,193		1,911
90 days or more past due	14,452		32,830
Total past due	19,479		38,529
Current	8,006,453		8,040,342
Total	8,025,932		8,078,871
Domestic | Construction and real estate	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	5,412		11,815
60-89 days past due	3,440		4,038
90 days or more past due	44,852		69,333
Total past due	53,704		85,186
Current	7,150,890		7,392,667
Total	7,204,594		7,477,853
Domestic | Services	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	2,185		3,385
60-89 days past due	1,235		1,916
90 days or more past due	10,304		13,829
Total past due	13,724		19,130
Current	3,943,018		3,952,881
Total	3,956,742		3,972,011
Domestic | Wholesale and retail	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	3,205		2,771
60-89 days past due	4,561		2,851
90 days or more past due	12,180		16,483
Total past due	19,946		22,105
Current	5,330,761		5,333,869
Total	5,350,707		5,355,974
Domestic | Transportation and communications	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	832		711
60-89 days past due	573		558
90 days or more past due	3,265		3,687
Total past due	4,670		4,956
Current	3,242,724		3,142,150
Total	3,247,394		3,147,106
Domestic | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
60-89 days past due	1		'
90 days or more past due	5		6
Total past due	6		6
Current	3,460,141		3,142,992
Total	3,460,147		3,142,998
Domestic | Government and public institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Current	6,734,451		6,907,426
Total	6,734,451		6,907,426
Domestic | Other industries	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	9		'
60-89 days past due	29		18
90 days or more past due	34		122
Total past due	72		140
Current	4,983,749		4,521,854
Total	4,983,821	[2]	4,521,994	[2]
Domestic | Individuals	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	38,466		41,987
60-89 days past due	18,488		24,114
90 days or more past due	56,605		69,774
Total past due	113,559		135,875
Current	11,860,960		11,840,205
Total	11,974,519		11,976,080
Foreign	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
30-59 days past due	87		127
60-89 days past due	23		885
90 days or more past due	10,935		11,132
Total past due	11,045		12,144
Current	18,674,188		15,353,007
Total	18,685,233		15,365,151
Foreign | Banks and other financial institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Total	4,610,141		4,088,651
Foreign | Government and public institutions	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Total	¥ 883,004		¥ 595,911
[1]	Amounts represent loan balances before deducting unearned income and deferred loan fees.
[2]	Other industries of domestic and Other of foreign include trade receivables and lease receivables of consolidated VIEs.

Changes_in_Allowance_for_Loan_

Changes in Allowance for Loan Losses (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'		'
Balance at beginning of fiscal year	¥ 772,957		¥ 682,692		¥ 734,530
Provision (credit) for loan losses	-126,230		139,947		-23,044
Charge-offs	65,148		94,597		80,142
Less: Recoveries	26,535		31,700		52,256
Net charge-offs	38,613		62,897		27,886
Others	18,063	[1]	13,215	[1]	-908	[1]
Balance at end of fiscal year	626,177		772,957		682,692
Allowance for loan losses of which individually evaluated for impairment	349,308		422,684		'
Allowance for loan losses of which collectively evaluated for impairment	276,869		350,273		'
Loans	73,623,540	[2]	69,945,464	[2]	'
Loans of which individually evaluated for impairment	1,194,315	[2]	1,266,424	[2]	'
Loans of which collectively evaluated for impairment	72,429,225	[2]	68,679,040	[2]	'
Corporate	'		'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'		'
Balance at beginning of fiscal year	641,895		535,475		563,116
Provision (credit) for loan losses	-128,368		137,549		-19,433
Charge-offs	47,927		69,845		54,599
Less: Recoveries	21,423		27,447		48,354
Net charge-offs	26,504		42,398		6,245
Others	14,326	[1]	11,269	[1]	-1,963	[1]
Balance at end of fiscal year	501,349		641,895		535,475
Allowance for loan losses of which individually evaluated for impairment	327,011		398,622		'
Allowance for loan losses of which collectively evaluated for impairment	174,338		243,273		'
Loans	54,651,867	[2]	51,801,814	[2]	'
Loans of which individually evaluated for impairment	1,100,938	[2]	1,160,489	[2]	'
Loans of which collectively evaluated for impairment	53,550,929	[2]	50,641,325	[2]	'
Retail	'		'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'		'
Balance at beginning of fiscal year	109,189		126,276		151,342
Provision (credit) for loan losses	-12,712		-14,180		-21,375
Charge-offs	3,935		4,249		5,133
Less: Recoveries	3,000		1,342		1,442
Net charge-offs	935		2,907		3,691
Balance at end of fiscal year	95,542		109,189		126,276
Allowance for loan losses of which individually evaluated for impairment	11,735		14,815		'
Allowance for loan losses of which collectively evaluated for impairment	83,807		94,374		'
Loans	12,922,564	[2]	13,007,792	[2]	'
Loans of which individually evaluated for impairment	39,250	[2]	45,961	[2]	'
Loans of which collectively evaluated for impairment	12,883,314	[2]	12,961,831	[2]	'
Other	'		'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'		'
Balance at beginning of fiscal year	21,873		20,941		20,072
Provision (credit) for loan losses	14,850		16,578		17,764
Charge-offs	13,286		20,503		20,410
Less: Recoveries	2,112		2,911		2,460
Net charge-offs	11,174		17,592		17,950
Others	3,737	[1]	1,946	[1]	1,055	[1]
Balance at end of fiscal year	29,286		21,873		20,941
Allowance for loan losses of which individually evaluated for impairment	10,562		9,247		'
Allowance for loan losses of which collectively evaluated for impairment	18,724		12,626		'
Loans	6,049,109	[2]	5,135,858	[2]	'
Loans of which individually evaluated for impairment	54,127	[2]	59,974	[2]	'
Loans of which collectively evaluated for impairment	¥ 5,994,982	[2]	¥ 5,075,884	[2]	'
[1]	Others include primarily foreign exchange translation.
[2]	Amounts represent loan balances before deducting unearned income and deferred loan fees.

Allowance_For_Loan_Losses_Addi

Allowance For Loan Losses - Additional Information (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Increase (Decrease) in provision for loan losses	¥ (266,177)	¥ 162,991	¥ (23,691)

Premises_and_Equipment_Detail

Premises and Equipment (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Land	¥ 410,739	¥ 268,948
Buildings	800,680	743,473
Equipment and furniture	435,655	418,647
Leasehold improvements	92,052	90,306
Construction in progress	35,789	23,875
Software	725,287	657,702
Total	2,500,202	2,202,951
Less: Accumulated depreciation and amortization	1,143,608	1,110,962
Premises and equipment-net	¥ 1,356,594	¥ 1,091,989

Premises_and_Equipment_Additio

Premises and Equipment - Additional Information (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Property, Plant and Equipment [Line Items]	'	'	'
Depreciation and amortization	¥ 155,549	¥ 151,550	¥ 160,231
Premises and equipment under capital leases, accumulated depreciation and amortization	1,143,608	1,110,962	'
Premises and equipment under capital leases	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Premises and equipment under capital leases	51,681	49,727	'
Premises and equipment under capital leases, accumulated depreciation and amortization	¥ 28,209	¥ 27,830	'

Changes_in_Goodwill_Detail

Changes in Goodwill (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013	Mar. 31, 2012
Goodwill [Line Items]	'		'	'
Balance at beginning of fiscal year	¥ 6,147		¥ 5,635	¥ 7,610
Goodwill acquired	7,719	[1]	'	3,776	[2]
Impairment losses recognized	3,792		'	5,637
Foreign exchange translation	1,475		512	-114
Balance at end of fiscal year	11,549		6,147	5,635
Gross amount of goodwill	80,615		71,421	70,909
Accumulated impairment losses	69,066		65,274	65,274
Mizuho Bank Limited	'		'	'
Goodwill [Line Items]	'		'	'
Balance at beginning of fiscal year	6,147		5,635	7,610
Goodwill acquired	7,719	[1]	'	3,776	[2]
Impairment losses recognized	3,792		'	5,637
Foreign exchange translation	1,475		512	-114
Balance at end of fiscal year	11,549		6,147	5,635
Gross amount of goodwill	80,615		71,421	70,909
Accumulated impairment losses	¥ 69,066		¥ 65,274	¥ 65,274
[1]	Goodwill acquired is entirely related to the acquisition of Banco Mizuho do Brasil S.A.
[2]	Goodwill acquired is entirely related to the acquisition of PT. Mizuho Balimor Finance.

Recovered_Sheet2

Goodwill and Intangible Assets - Additional Information (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Goodwill and Intangible Assets Disclosure [Line Items]	'	'	'
Goodwill impairment losses recognized	¥ 3,792	'	¥ 5,637
Intangible assets amortization expenses recognized	¥ 5,709	¥ 5,615	¥ 5,490

Gross_Carrying_Amount_Accumula

Gross Carrying Amount Accumulated Amortization and Net Carrying Amount of Intangible Assets (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Intangible Assets by Major Class [Line Items]	'		'
Gross carrying amount	¥ 76,757		¥ 76,312
Gross carrying amount	9,207		9,450
Net carrying amount	9,207		9,450
Gross carrying amount	85,964		85,762
Accumulated amortization	27,017		21,288
Net carrying amount	49,740		55,024
Net carrying amount	58,947		64,474
Customer relationships	'		'
Intangible Assets by Major Class [Line Items]	'		'
Gross carrying amount	73,949	[1]	73,949	[1]
Accumulated amortization	24,865	[1]	19,238	[1]
Net carrying amount	49,084	[1]	54,711	[1]
Other	'		'
Intangible Assets by Major Class [Line Items]	'		'
Gross carrying amount	2,808		2,363
Accumulated amortization	2,152		2,050
Net carrying amount	¥ 656		¥ 313
[1]	Customer relationships were acquired by the merger of MHSC and Shinko on May 7, 2009. See Note 1 "Basis of presentation and summary of significant accounting policies" for further information.

Estimated_Aggregate_Amortizati

Estimated Aggregate Amortization Expenses for Intangible Assets (Detail) (JPY ¥)	Mar. 31, 2014
In Millions, unless otherwise specified
Expected Amortization Expense [Line Items]	'
2015	¥ 5,349
2016	5,058
2017	4,780
2018	4,502
2019	¥ 4,264

Amounts_Pledged_as_Collateral_

Amounts Pledged as Collateral for Borrowings and for Other Purposes (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Financial Instruments Owned and Pledged as Collateral [Line Items]	'	'
Interest-bearing deposits in other banks	¥ 38	¥ 28
Trading account assets	10,271	13,752
Available-for-sale securities	13,353	15,939
Loans	8,796	8,860
Other assets	677	900
Total	¥ 33,135	¥ 39,479

Associated_Liabilities_Collate

Associated Liabilities Collateralized by Pledged Assets (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]	'	'
Deposits	¥ 878	¥ 259
Call money and funds purchased	1,708	1,580
Payables under repurchase agreements	6,884	7,726
Payables under securities lending transactions	6,237	11,092
Other short-term borrowings	405	5,626
Long-term debt	5,632	321
Total	¥ 21,744	¥ 26,604

Recovered_Sheet3

Pledged Assets and Collateral - Additional Information (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items]	'	'
Reserve funds maintained with the BOJ	¥ 18,084	¥ 10,507
Reserve funds requires to be maintained by MHFG Group	1,184	1,099
Fair value collateral received that can be sold or repledged	13,817	15,501
Fair value collateral received that can be sold or repledged, value of collateral sold or repledged	¥ 12,508	¥ 13,834

Balances_of_Time_Deposits_and_

Balances of Time Deposits and Certificates of Deposit Issued by Domestic Offices in Amounts of Yen Ten Million or more and Balances of those Deposits Issued by Foreign Offices in Amounts of United States One Hundred Thousand Dollars or more (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, unless otherwise specified
Deposits From Banking Clients [Line Items]	'	'
Domestic deposit in amounts of YEN 10 million or more	¥ 26,469,338	¥ 29,695,290
Foreign deposit in amounts of USD 100,000 or more	14,193,833	12,142,704
Time deposits	'	'
Deposits From Banking Clients [Line Items]	'	'
Domestic deposit in amounts of YEN 10 million or more	18,351,826	18,302,196
Foreign deposit in amounts of USD 100,000 or more	9,555,568	8,209,016
Certificates of deposit	'	'
Deposits From Banking Clients [Line Items]	'	'
Domestic deposit in amounts of YEN 10 million or more	8,117,512	11,393,094
Foreign deposit in amounts of USD 100,000 or more	¥ 4,638,265	¥ 3,933,688

Deposits_Additional_Informatio

Deposits - Additional Information (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Deposits From Banking Clients [Line Items]	'	'
Aggregate amount of demand deposits in overdraft status that have been reclassified as loan balances	¥ 597	¥ 543

Balance_and_Remaining_Maturiti

Balance and Remaining Maturities of Time Deposits and Certificates of Deposit Issued by Domestic and Foreign Offices (Detail) (JPY ¥)	Mar. 31, 2014
In Millions, unless otherwise specified
Deposits From Banking Clients [Line Items]	'
Total	¥ 50,440,210
Domestic	'
Deposits From Banking Clients [Line Items]	'
Due in one year or less	32,195,172
Due after one year through two years	1,912,770
Due after two years through three years	1,243,980
Due after three years through four years	342,948
Due after four years through five years	412,261
Due after five years	133,735
Total	36,240,866
Foreign	'
Deposits From Banking Clients [Line Items]	'
Due in one year or less	14,157,187
Due after one year through two years	27,895
Due after two years through three years	9,528
Due after three years through four years	1,102
Due after four years through five years	3,240
Due after five years	392
Total	14,199,344
Time deposits	'
Deposits From Banking Clients [Line Items]	'
Total	37,684,433
Time deposits | Domestic	'
Deposits From Banking Clients [Line Items]	'
Due in one year or less	24,079,640
Due after one year through two years	1,910,790
Due after two years through three years	1,243,980
Due after three years through four years	342,948
Due after four years through five years	412,261
Due after five years	133,735
Total	28,123,354
Time deposits | Foreign	'
Deposits From Banking Clients [Line Items]	'
Due in one year or less	9,526,641
Due after one year through two years	20,176
Due after two years through three years	9,528
Due after three years through four years	1,102
Due after four years through five years	3,240
Due after five years	392
Total	9,561,079
Certificates of deposit	'
Deposits From Banking Clients [Line Items]	'
Total	12,755,777
Certificates of deposit | Domestic	'
Deposits From Banking Clients [Line Items]	'
Due in one year or less	8,115,532
Due after one year through two years	1,980
Total	8,117,512
Certificates of deposit | Foreign	'
Deposits From Banking Clients [Line Items]	'
Due in one year or less	4,630,546
Due after one year through two years	7,719
Total	¥ 4,638,265

Details_of_Other_ShortTerm_Bor

Details of Other Short-Term Borrowings (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Short-term Debt [Line Items]	'		'
Short-term notes	¥ 497,100	[1]	¥ 477,400	[1]
Borrowings from the Bank of Japan	5,138,003		5,884,304
Other	101,901		110,119
Total	6,023,972		6,724,100
Consolidated VIEs	'		'
Short-term Debt [Line Items]	'		'
Commercial paper and short-term notes issued	286,968	[1],[2]	252,277	[1],[2]
Short-term notes	87,468		88,083
Total	¥ 287,910		¥ 253,311
[1]	Short-term notes are issued under laws of Japan in the form of dematerialized commercial paper, whose characteristics are economically the same as commercial paper.
[2]	Commercial paper and short-term notes issued by consolidated VIEs of asset-backed commercial paper programs in the above table consist of commercial paper and short-term notes, of which amounts were ¥164,194 million and ¥88,083 million, respectively, at March 31, 2013, and ¥199,500 million and ¥87,468 million, respectively, at March 31, 2014.

Details_of_Other_ShortTerm_Bor1

Details of Other Short-Term Borrowings (Parenthetical) (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Short-term Debt [Line Items]	'		'
Short-term notes	¥ 497,100	[1]	¥ 477,400	[1]
Consolidated VIEs	'		'
Short-term Debt [Line Items]	'		'
Commercial paper	199,500		164,194
Short-term notes	¥ 87,468		¥ 88,083
[1]	Short-term notes are issued under laws of Japan in the form of dematerialized commercial paper, whose characteristics are economically the same as commercial paper.

LongTerm_Debt_with_Original_Ma

Long-Term Debt with Original Maturities of More Than One Year (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, unless otherwise specified
Debt Instrument [Line Items]	'	'
Obligations under capital leases	¥ 26,680	¥ 24,406
Loan participation borrowings	79,014	62,332
Senior borrowings and bonds	5,805,634	4,784,010
Subordinated borrowings and bonds	3,942,613	3,931,475
Total	¥ 9,853,941	¥ 8,802,223

Interest_Rates_and_Maturities_

Interest Rates and Maturities of Senior Borrowings and Bonds and Subordinated Borrowings and Bonds (Detail) (JPY ¥)

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

In Millions, unless otherwise specified

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Minimum

Minimum

Minimum

Minimum

Minimum

Minimum

Minimum

Minimum

Minimum

Maximum

Maximum

Maximum

Maximum

Maximum

Maximum

Maximum

Maximum

Maximum

Fixed Rate

Fixed Rate

Fixed Rate

Fixed Rate

Fixed Rate

Fixed Rate

Floating Rate

Floating Rate

Floating Rate

Floating Rate

Floating Rate

Floating Rate

Fixed Rate

Fixed Rate

Fixed Rate

Fixed Rate

Floating Rate

Floating Rate

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Senior borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Subordinated borrowings and bonds

Denominated in Japanese yen

Denominated in Japanese yen

Denominated in U.S. dollars

Denominated in U.S. dollars

Denominated in other currencies

Denominated in other currencies

Denominated in Japanese yen

Denominated in Japanese yen

Denominated in U.S. dollars

Denominated in U.S. dollars

Denominated in other currencies

Denominated in other currencies

Denominated in Japanese yen

Denominated in Japanese yen

Denominated in U.S. dollars

Denominated in U.S. dollars

Denominated in Japanese yen

Denominated in Japanese yen

Fixed Rate

Fixed Rate

Fixed Rate

Floating Rate

Floating Rate

Floating Rate

Fixed Rate

Fixed Rate

Floating Rate

Fixed Rate

Fixed Rate

Fixed Rate

Floating Rate

Floating Rate

Floating Rate

Fixed Rate

Fixed Rate

Floating Rate

Denominated in Japanese yen

Denominated in U.S. dollars

Denominated in other currencies

Denominated in Japanese yen

Denominated in U.S. dollars

Denominated in other currencies

Denominated in Japanese yen

Denominated in U.S. dollars

Denominated in Japanese yen

Denominated in Japanese yen

Denominated in U.S. dollars

Denominated in other currencies

Denominated in Japanese yen

Denominated in U.S. dollars

Denominated in other currencies

Denominated in Japanese yen

Denominated in U.S. dollars

Denominated in Japanese yen

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rates

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.00%

[1]

0.00%

[1]

0.02%

[1]

0.00%

[1]

0.00%

[1]

0.05%

[1]

1.09%

[1]

4.30%

[1]

0.98%

[1]

10.00%

[1]

7.49%

[1]

5.40%

[1]

18.10%

[1]

15.60%

[1]

0.58%

[1]

4.74%

[1]

14.91%

[1]

2.61%

[1]

Maturities

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'2014-04

[2]

'2014-04

[2]

'2015-01

[2]

'2014-04

[2]

'2014-04

[2]

'2014-04

[2]

'2014-04

[2]

'2014-04

[2]

'2019-06

[2]

'2044-03

[2]

'2043-07

[2]

'2029-03

[2]

'2044-03

[2]

'2028-03

[2]

'2015-01

[2]

'Perpetual

[2]

'Perpetual

[2]

'Perpetual

[2]

Borrowings and bonds

¥ 9,748,247

¥ 8,715,485

¥ 5,805,634

¥ 4,784,010

¥ 3,557,508

¥ 2,741,475

¥ 604,281

¥ 520,714

¥ 25,687

¥ 683

¥ 1,063,111

¥ 1,065,708

¥ 532,199

¥ 426,515

¥ 22,848

¥ 28,915

¥ 3,942,613

¥ 3,931,475

¥ 3,249,999

¥ 3,393,092

¥ 613,609

¥ 419,383

¥ 79,005

¥ 119,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[1]

The interest rates disclosed reflect the range of contractual rates in effect at March 31, 2014.

[2]

Maturity information disclosed is the range of maturities at March 31, 2014.

Contractual_Maturities_of_Long

Contractual Maturities of Long-term Debt (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, unless otherwise specified
Debt Instrument [Line Items]	'	'
2015	¥ 1,222,317	'
2016	1,190,985	'
2017	1,776,546	'
2018	1,025,441	'
2019	483,888	'
2020 and thereafter	4,154,764	'
Total	¥ 9,853,941	¥ 8,802,223

Other_Assets_and_Liabilities_D

Other Assets and Liabilities (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, unless otherwise specified
Other assets:	'	'
Accounts receivable from brokers, dealers and customers for securities transactions	¥ 1,122,247	¥ 907,671
Collateral provided for derivative transactions	466,420	742,307
Prepaid pension cost	403,654	153,414
Miscellaneous receivables	315,037	120,322
Margins provided for futures contracts	147,376	99,844
Security deposits	121,675	102,031
Loans held for sale	58,745	9,820
Other	563,841	466,542
Total	3,198,995	2,601,951
Other liabilities:	'	'
Accounts payable to brokers, dealers and customers for securities transactions	1,325,455	1,560,345
Guaranteed trust principal	591,647	535,720
Miscellaneous payables	473,028	260,665
Collateral accepted for derivative transactions	432,820	503,101
Factoring amounts owed to customers	382,189	375,933
Margins accepted for futures contracts	289,381	199,930
Unearned income	141,735	141,189
Other	785,768	791,243
Total	¥ 4,422,023	¥ 4,368,126

Composition_of_Preferred_Stock

Composition of Preferred Stock (Detail) (JPY ¥)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Class of Stock [Line Items]	'		'		'
Aggregate amount	¥ 914,752		¥ 951,442		¥ 951,442
Number of shares Authorized	4,251,442,000		4,369,512,000		4,369,512,000
Number of shares Issued	914,752,000		951,442,000		951,442,000
Number of shares In treasury	13,817,747		22,128,230		'
Eleventh series class XI preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Aggregate amount	914,752	[1]	914,752	[1]	914,752	[1]
Number of shares Authorized	914,752,000	[1]	1,369,512,000	[1]	1,369,512,000	[1]
Number of shares Issued	914,752,000	[1]	914,752,000	[1]	914,752,000	[1]
Liquidation value per share	¥ 1,000	[1]	¥ 1,000	[1]	¥ 1,000	[1]
Convertible or not	'Yes	[1]	'Yes	[1]	'Yes	[1]
Class XII preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	'		1,500,000,000		1,500,000,000
Convertible or not	'		'-		'-
Thirteenth series class XIII preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Aggregate amount	'		¥ 36,690		¥ 36,690
Number of shares Authorized	36,690,000		1,500,000,000		1,500,000,000
Number of shares Issued	'		36,690,000		36,690,000
Liquidation value per share	'		¥ 1,000		¥ 1,000
Convertible or not	'-		'No		'No
First series class XIV preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	900,000,000	[2]	'		'
Convertible or not	'-	[2]	'		'
Second series class XIV preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	900,000,000	[2]	'		'
Convertible or not	'-	[2]	'		'
Third series class XIV preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	900,000,000	[2]	'		'
Convertible or not	'-	[2]	'		'
Fourth series class XIV preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	900,000,000	[2]	'		'
Convertible or not	'-	[2]	'		'
First series class XV preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	900,000,000	[3]	'		'
Convertible or not	'-	[3]	'		'
Second series class XV preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	900,000,000	[3]	'		'
Convertible or not	'-	[3]	'		'
Third series class XV preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	900,000,000	[3]	'		'
Convertible or not	'-	[3]	'		'
Fourth series class XV preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	900,000,000	[3]	'		'
Convertible or not	'-	[3]	'		'
First series class XVI preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	1,500,000,000	[4]	'		'
Convertible or not	'-	[4]	'		'
Second series class XVI preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	1,500,000,000	[4]	'		'
Convertible or not	'-	[4]	'		'
Third series class XVI preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	1,500,000,000	[4]	'		'
Convertible or not	'-	[4]	'		'
Fourth series class XVI preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares Authorized	1,500,000,000	[4]	'		'
Convertible or not	'-	[4]	'		'
Preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares In treasury	602,100,700		574,087,800		541,073,800
Preferred stock | Eleventh series class XI preferred stock	'		'		'
Class of Stock [Line Items]	'		'		'
Number of shares In treasury	602,100,700	[1]	574,087,800	[1]	541,073,800	[1]
[1]	The aggregate amount and number of issued shares include the preferred stock in treasury which has been converted to common stock but not yet cancelled.
[2]	The total number of authorized shares from first to fourth series class XIV preferred stock shall not exceed 900,000,000.
[3]	The total number of authorized shares from first to fourth series class XV preferred stock shall not exceed 900,000,000.
[4]	The total number of authorized shares from first to fourth series class XVI preferred stock shall not exceed 1,500,000,000.

Composition_of_Preferred_Stock1

Composition of Preferred Stock (Parenthetical) (Detail)	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Class of Stock [Line Items]	'	'	'
Number of shares Authorized	4,251,442,000	4,369,512,000	4,369,512,000
First to fourth series class XIV Preferred Stock | Maximum	'	'	'
Class of Stock [Line Items]	'	'	'
Number of shares Authorized	900,000,000	'	'
First to fourth series class XV Preferred Stock | Maximum	'	'	'
Class of Stock [Line Items]	'	'	'
Number of shares Authorized	900,000,000	'	'
First to fourth series class XVI Preferred Stock | Maximum	'	'	'
Class of Stock [Line Items]	'	'	'
Number of shares Authorized	1,500,000,000	'	'

Material_Terms_and_Conditions_

Material Terms and Conditions Conversion of Eleventh Series Class XI Preferred Stock (Detail) (Eleventh series class XI preferred stock)	12 Months Ended
	Mar. 31, 2014
Class of Stock [Line Items]	'
Conversion ratio	'¥1,000/(conversion price), where the conversion price after adjustment is ¥282.90 on or after August 30, 2011; to be reset on July 1, 2014 and 2015 (each, a "Reset Date") as ¥1,000/(conversion price), where the conversion price is the lower of (x) the average price of daily closing prices (including closing bid or offered price) of common stock as reported by the Tokyo Stock Exchange ("TSE") for the 30 consecutive trading days (excluding trading days on which no closing price, closing bid or offered price is reported) commencing on the 45th trading day prior to the Reset Date and (y) the conversion price after adjustment effective as of the day before the relevant Reset Date, provided that the conversion price shall not be less than ¥282.90.	[1]
Minimum	'
Class of Stock [Line Items]	'
Conversion period	1-Jul-08
Maximum	'
Class of Stock [Line Items]	'
Conversion period	30-Jun-16
[1]	Subject to adjustment, where issuance or disposal by MHFG of common stock for a price below the "current market price", a stock split, issuance of securities convertible into common stock at a price below the "current market price" at the time of issuance thereof or determination of the conversion price thereof, merger or amalgamation, or a capital decrease or stock consolidation occurs and in certain other circumstances.

Material_Terms_and_Conditions_1

Material Terms and Conditions Conversion of Eleventh Series Class XI Preferred Stock (Parenthetical) (Detail) (Eleventh series class XI preferred stock, JPY ¥)	Mar. 31, 2014
Eleventh series class XI preferred stock	'
Class of Stock [Line Items]	'
Conversion price, numerator	¥ 1,000
Conversion price, denominator	¥ 282.9

Material_Terms_and_Conditions_2

Material Terms and Conditions Conversion of Eleventh Series Class XI Preferred Stock on Day Following End of Conversion Period (Detail) (Eleventh series class XI preferred stock)	12 Months Ended
	Mar. 31, 2014
Class of Stock [Line Items]	'
Conversion ratio	'¥1,000/(conversion price), where the conversion price after adjustment is ¥282.90 on or after August 30, 2011; to be reset on July 1, 2014 and 2015 (each, a "Reset Date") as ¥1,000/(conversion price), where the conversion price is the lower of (x) the average price of daily closing prices (including closing bid or offered price) of common stock as reported by the Tokyo Stock Exchange ("TSE") for the 30 consecutive trading days (excluding trading days on which no closing price, closing bid or offered price is reported) commencing on the 45th trading day prior to the Reset Date and (y) the conversion price after adjustment effective as of the day before the relevant Reset Date, provided that the conversion price shall not be less than ¥282.90.	[1]
Conversion on the day following the end of the conversion period	'
Class of Stock [Line Items]	'
Conversion date	1-Jul-16
Conversion ratio	'¥1,000/(current market price), where the current market price is the average price of daily closing prices (including closing bid or offered price) of common stock as reported by the TSE for the 30 consecutive trading days (excluding trading days on which no closing price, closing bid or offered price is reported) commencing on the 45th trading day prior to July 1, 2016, provided that the current market price shall not be less than ¥282.90.
[1]	Subject to adjustment, where issuance or disposal by MHFG of common stock for a price below the "current market price", a stock split, issuance of securities convertible into common stock at a price below the "current market price" at the time of issuance thereof or determination of the conversion price thereof, merger or amalgamation, or a capital decrease or stock consolidation occurs and in certain other circumstances.

Material_Terms_and_Conditions_3

Material Terms and Conditions Conversion of Eleventh Series Class XI Preferred Stock on Day Following End of Conversion Period (Parenthetical) (Detail) (Eleventh series class XI preferred stock, JPY ¥)	Mar. 31, 2014
Eleventh series class XI preferred stock	'
Class of Stock [Line Items]	'
Conversion price, numerator	¥ 1,000
Conversion price, denominator	¥ 282.9

Changes_in_Number_of_Shares_an

Changes in Number of Shares and Aggregate Amount of Preferred Stock (Detail) (JPY ¥)

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2012

Mar. 31, 2014

Mar. 31, 2012

Mar. 31, 2011

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2012

Mar. 31, 2011

Mar. 31, 2014

Mar. 31, 2012

Mar. 31, 2011

Mar. 31, 2014

Mar. 31, 2012

Mar. 31, 2011

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2012

Mar. 31, 2011

Mar. 31, 2014

Mar. 31, 2012

Mar. 31, 2011

In Millions, except Share data, unless otherwise specified

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Preferred stock

Eleventh series class XI preferred stock

Eleventh series class XI preferred stock

Eleventh series class XI preferred stock

Eleventh series class XI preferred stock

Thirteenth series class XIII preferred stock

Thirteenth series class XIII preferred stock

Thirteenth series class XIII preferred stock

Stock Issued

Stock Issued

Stock Issued

Stock Issued

Stock Issued

Stock Issued

Stock Issued

Stock Issued

Stock Issued

Stock Issued

Eleventh series class XI preferred stock

Eleventh series class XI preferred stock

Eleventh series class XI preferred stock

Eleventh series class XI preferred stock

Thirteenth series class XIII preferred stock

Thirteenth series class XIII preferred stock

Thirteenth series class XIII preferred stock

Class of Stock [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Issued at beginning of year

'

'

'

951,442,000

951,442,000

951,442,000

914,752,000

[1]

914,752,000

[1]

914,752,000

[1]

914,752,000

[1]

36,690,000

36,690,000

36,690,000

'

'

'

'

'

'

'

'

'

'

Net change

'

'

'

-36,690,000

'

'

'

'

'

'

-36,690,000

'

'

'

'

'

'

'

'

'

'

'

'

Issued at end of year

'

'

'

914,752,000

951,442,000

951,442,000

914,752,000

[1]

914,752,000

[1]

914,752,000

[1]

914,752,000

[1]

'

36,690,000

36,690,000

'

'

'

'

'

'

'

'

'

'

Balance at beginning of fiscal year

¥ 6,621,371

¥ 5,857,095

¥ 4,647,024

¥ 377,354

¥ 410,368

¥ 453,576

'

'

'

'

'

'

'

¥ 951,442

¥ 951,442

¥ 951,442

¥ 914,752

[1]

¥ 914,752

[1]

¥ 914,752

[1]

¥ 914,752

[1]

¥ 36,690

¥ 36,690

¥ 36,690

Net change

'

'

'

'

'

'

'

'

'

'

'

'

'

-36,690

'

'

'

'

'

'

-36,690

'

'

Balance at end of fiscal year

¥ 6,621,371

¥ 5,857,095

¥ 4,647,024

¥ 312,651

¥ 410,368

¥ 453,576

'

'

'

'

'

'

'

¥ 914,752

¥ 951,442

¥ 951,442

¥ 914,752

[1]

¥ 914,752

[1]

¥ 914,752

[1]

¥ 914,752

[1]

'

¥ 36,690

¥ 36,690

[1]

The aggregate amount and number of issued shares include the preferred stock in treasury which has been converted to common stock but not yet cancelled.

Common_Stock_Additional_inform

Common Stock - Additional information (Detail) (JPY ¥)	12 Months Ended	0 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2012	Sep. 01, 2011	Sep. 01, 2011	Sep. 01, 2011
		Mizuho Trust & Banking Company Limited	The Former Mizuho Securities Company Limited	The Former Mizuho Investors Securities Company Limited
Class of Stock [Line Items]	'	'	'	'
Equity transaction, shares of common stock issued	4,748,000	824,271,984	951,166,005	322,928,897
Equity transaction, voting equity interests received in exchange	'	30.15%	40.80%	46.02%
Equity transaction, value of common stock issued	'	¥ 95,828	¥ 110,379	¥ 37,497
Equity transaction, increase (decrease) in additional paid-in capital to adjust the carrying amount of Noncontrolling interests	'	-65,494	38,423	11,599
Equity transaction, the carrying amount of Accumulated other comprehensive income adjusted to reflect the change in the ownership interest	'	¥ 958	¥ (2,178)	¥ 744

Changes_in_Number_of_Issued_Sh

Changes in Number of Issued Shares of Common Stock (Detail)	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Class of Stock [Line Items]	'	'	'
Balance at beginning of fiscal year	24,164,864,477	24,048,165,727	21,782,185,320
Issuance of new shares of common stock by conversion of Eleventh series class XI preferred stock	99,020,710	116,698,750	151,921,540
Issuance of new shares of common stock by exercise of stock acquisition rights	'	'	4,748,000
Issuance of new shares of common stock for stock exchanges	'	'	2,109,310,867
Balance at end of fiscal year	24,263,885,187	24,164,864,477	24,048,165,727

Dividends_Additional_Informati

Dividends - Additional Information (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2013
		Japan Gaap Additional Paid-in Capital	Japan Gaap Retained Earnings	Mar-14	Mar-14
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'	'	'	'	'
Capital stock	¥ 2,254,973	'	'	'	'
Capital surplus	1,194,865	'	'	'	'
Retained earnings	1,419,866	'	'	'	'
Description of dividend payment restrictions	'In making a distribution of retained earnings, an entity must set aside in its legal reserve an amount equal to one-tenth of the amount of retained earnings so distributed, until its legal reserve reaches to one-quarter of its capital stock.	'	'	'	'
Percentage of retained earnings set aside for legal reserve	10.00%	'	'	'	'
Legal reserve	1,199,215	1,194,865	4,350	'	'
Maximum amount available for dividends under Company Law and the Banking Law	¥ 1,412,282	'	'	'	'
Minimum Common Equity Tier 1 ratio required for capital adequacy purposes	4.50%	'	'	4.00%	3.50%

Dividends_on_Preferred_Stock_a

Dividends on Preferred Stock and Common Stock (Detail) (JPY ¥)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Japan Gaap Dividends Payable [Line Items]	'		'		'
Cash dividends In aggregate	¥ 152,265	[1]	¥ 152,722	[1]	¥ 216,508	[1],[2]
Eleventh series class XI preferred stock	'		'		'
Japan Gaap Dividends Payable [Line Items]	'		'		'
Cash dividends Per share	¥ 20		¥ 20		¥ 30	[2]
Cash dividends In aggregate	6,717	[1]	7,451	[1]	12,173	[1],[2]
Thirteenth series class XIII preferred stock	'		'		'
Japan Gaap Dividends Payable [Line Items]	'		'		'
Cash dividends Per share	¥ 15	[3]	¥ 30		¥ 45	[2]
Cash dividends In aggregate	550	[1],[3]	1,101	[1]	1,651	[1],[2]
Common stock	'		'		'
Japan Gaap Dividends Payable [Line Items]	'		'		'
Cash dividends Per share	¥ 6		¥ 6		¥ 9	[2]
Cash dividends In aggregate	¥ 144,998	[1]	¥ 144,170	[1]	¥ 202,684	[1],[2]
[1]	Dividends paid on treasury stock are excluded.
[2]	As MHFG commenced distributing an interim dividend from the fiscal year ended March 31, 2012, the amounts for the fiscal year include such interim dividends.
[3]	On July 11, 2013, MHFG acquired and cancelled all of the shares of the thirteenth series class XIII preferred stock. Consequently, the amount for the fiscal year does not include interim dividends.

Changes_in_Each_Component_of_A

Changes in Each Component of Accumulated Other Comprehensive Income (Loss), Net Of Tax (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Balance at beginning of fiscal year	¥ 777,997	¥ 245,588	¥ 104,972
Less: reclassification adjustments for losses (gains) included in net income	-122,606	'	'
Change during year	339,880	532,409	140,616
Balance at end of fiscal year	1,117,877	777,997	245,588
Accumulated Net Unrealized Investment Gain (Loss)	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Balance at beginning of fiscal year	995,124	628,636	514,128
Before reclassification adjustments during year	255,140	427,913	87,215
Less: reclassification adjustments for losses (gains) included in net income	-126,992	-61,425	27,293
Change during year	128,148	366,488	114,508
Balance at end of fiscal year	1,123,272	995,124	628,636
Accumulated Translation Adjustment	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Balance at beginning of fiscal year	-82,420	-169,881	-165,028
Before reclassification adjustments during year	75,986	87,460	-6,779
Less: reclassification adjustments for losses (gains) included in net income	'	1	1,926
Change during year	75,986	87,461	-4,853
Balance at end of fiscal year	-6,434	-82,420	-169,881
Accumulated Defined Benefit Plans Adjustment	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Balance at beginning of fiscal year	-134,707	-213,167	-244,128
Before reclassification adjustments during year	131,360	67,795	14,711
Less: reclassification adjustments for losses (gains) included in net income	4,386	10,665	16,250
Change during year	135,746	78,460	30,961
Balance at end of fiscal year	¥ 1,039	¥ (134,707)	¥ (213,167)

Amounts_Reclassified_Out_of_Ac

Amounts Reclassified Out of Accumulated Other Comprehensive Income (Loss) into Net Income (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013	Mar. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'		'	'
Before tax	¥ 190,347	[1]	'	'
Tax effect	-67,786	[2]	'	'
Net of tax before allocation to noncontrolling interests	122,561		'	'
Net of tax attributable to noncontrolling interests	-45	[2]	'	'
Net of tax attributable to MHFG shareholders	122,606		'	'
Accumulated Net Unrealized Investment Gain (Loss)	'		'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'		'	'
Net of tax attributable to MHFG shareholders	126,992		61,425	-27,293
Accumulated Net Unrealized Investment Gain (Loss) | Investment gains (losses)-net	'		'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'		'	'
Before tax	197,224	[1]	'	'
Tax effect	-70,228	[2]	'	'
Net of tax before allocation to noncontrolling interests	126,996		'	'
Net of tax attributable to noncontrolling interests	4	[2]	'	'
Net of tax attributable to MHFG shareholders	126,992		'	'
Accumulated Defined Benefit Plans Adjustment	'		'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'		'	'
Net of tax attributable to MHFG shareholders	-4,386		-10,665	-16,250
Accumulated Defined Benefit Plans Adjustment | Salaries and employee benefits	'		'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'		'	'
Before tax	-6,877	[1]	'	'
Tax effect	2,442	[2]	'	'
Net of tax before allocation to noncontrolling interests	-4,435		'	'
Net of tax attributable to noncontrolling interests	-49	[2]	'	'
Net of tax attributable to MHFG shareholders	¥ (4,386)		'	'
[1]	The amounts in the Before tax column are recorded in each account presented as "Affected line items in the consolidated statements of income".
[2]	The amounts in the Tax effect column and Net of tax attributable to noncontrolling interests column are recorded in Income tax expense and Net income attributable to noncontrolling interests in the consolidated statements of income respectively.

Regulatory_Matters_Additional_

Regulatory Matters - Additional Information (Detail) (JPY ¥)	12 Months Ended
In Billions, unless otherwise specified	Mar. 31, 2014
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Capital adequacy ratio	120.00%
Common Equity Tier 1 capital requirement, including capital conservation buffer	7.00%
Increments of capital investment	10.00%
Additional Tier 1 capital	¥ 1,666.5
Tier 2 capital	¥ 1,349.6
Additional loss absorbency	1.00%
Adjustment in the calculation of Common Equity	20.00%
Increased in Common Equity	20.00%
Date at which regulatory adjustments reach 100%	'2018-03
Description of regulatory actions for not maintaining the minimum capital ratio concerning securities subsidiaries	'A capital ratio of less than 140% will call for regulatory reporting and a capital ratio of less than 100% may lead to a temporary suspension of all or part of the business operations and further, to the cancellation of the license to act as a securities broker and dealer.
Minimum	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Buffer ranging percentage	0.00%
Minimum | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Capital adequacy ratio	1.00%
Minimum | Capital ratio that call for regulatory reporting	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Capital adequacy ratio	140.00%
Minimum | Capital ratio that lead to a temporary suspension of all or part of the business operations and cancellation of the license to act as a securities broker and dealer	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Capital adequacy ratio	100.00%
Maximum	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Buffer ranging percentage	2.50%
Maximum | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Capital adequacy ratio	2.50%
Basel III	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Tier 1 capital ratio	6.00%
Common Equity Tier 1	4.50%
Basel III | Minimum	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Capital adequacy ratio	8.00%
Mar-13	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Common Equity Tier 1	3.50%
March 2013 | Basel III	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Tier 1 capital ratio	4.50%
Common Equity Tier 1	3.50%
March 2014 | Basel III	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Tier 1 capital ratio	5.50%
Common Equity Tier 1	4.00%
Mar-15	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Common Equity Tier 1	4.50%
Mar-16	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Capital conservation buffer	0.63%
Mar-19	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements [Line Items]	'
Common Equity Tier 1 capital requirement, including capital conservation buffer	7.00%

Capital_Requirements_and_Regul

Capital Requirements and Regulatory Adjustments Over Transitional Period (Detail)	12 Months Ended
	Mar. 31, 2014
Mar-13	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	0.00%
Phase out of recognition of capital instruments that no longer qualify as capital	90.00%	[1]
Phase-in of deductions from capital	0.00%	[1]
March 2013 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	3.50%	[1]
March 2013 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.50%	[1]
March 2013 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'-
Mar-14	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	0.00%
Phase out of recognition of capital instruments that no longer qualify as capital	80.00%	[1]
Phase-in of deductions from capital	20.00%	[1]
March 2014 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.00%	[1]
March 2014 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	5.50%	[1]
March 2014 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'-
Mar-15	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	0.00%
Phase out of recognition of capital instruments that no longer qualify as capital	70.00%	[1]
Phase-in of deductions from capital	40.00%	[1]
March 2015 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.50%	[1]
March 2015 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	6.00%	[1]
March 2015 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'-
Mar-16	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	0.63%
Phase out of recognition of capital instruments that no longer qualify as capital	60.00%	[1]
Phase-in of deductions from capital	60.00%	[1]
March 2016 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.50%	[1]
March 2016 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	6.00%	[1]
March 2016 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'Additional loss absorption capacity tailored to the impact of the entity's default, ranging from 1% to 2.5% of risk-weighted assets, to be met with Common Equity Tier 1 capital
Mar-17	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	1.25%
Phase out of recognition of capital instruments that no longer qualify as capital	50.00%	[1]
Phase-in of deductions from capital	80.00%	[1]
March 2017 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.50%	[1]
March 2017 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	6.00%	[1]
March 2017 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'Additional loss absorption capacity tailored to the impact of the entity's default, ranging from 1% to 2.5% of risk-weighted assets, to be met with Common Equity Tier 1 capital
Mar-18	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	1.88%
Phase out of recognition of capital instruments that no longer qualify as capital	40.00%	[1]
Phase-in of deductions from capital	100.00%	[1]
March 2018 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.50%	[1]
March 2018 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	6.00%	[1]
March 2018 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'Additional loss absorption capacity tailored to the impact of the entity's default, ranging from 1% to 2.5% of risk-weighted assets, to be met with Common Equity Tier 1 capital
Mar-19	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	2.50%
Phase out of recognition of capital instruments that no longer qualify as capital	30.00%	[1]
Phase-in of deductions from capital	100.00%	[1]
March 2019 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.50%	[1]
March 2019 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	6.00%	[1]
March 2019 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'Additional loss absorption capacity tailored to the impact of the entity's default, ranging from 1% to 2.5% of risk-weighted assets, to be met with Common Equity Tier 1 capital
Mar-20	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	2.50%
Phase out of recognition of capital instruments that no longer qualify as capital	20.00%	[1]
Phase-in of deductions from capital	100.00%	[1]
March 2020 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.50%	[1]
March 2020 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	6.00%	[1]
March 2020 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'Additional loss absorption capacity tailored to the impact of the entity's default, ranging from 1% to 2.5% of risk-weighted assets, to be met with Common Equity Tier 1 capital
Mar-21	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	2.50%
Phase out of recognition of capital instruments that no longer qualify as capital	10.00%	[1]
Phase-in of deductions from capital	100.00%	[1]
March 2021 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.50%	[1]
March 2021 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	6.00%	[1]
March 2021 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'Additional loss absorption capacity tailored to the impact of the entity's default, ranging from 1% to 2.5% of risk-weighted assets, to be met with Common Equity Tier 1 capital
Mar-22	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	8.00%	[1]
Capital conservation buffer	2.50%
Phase out of recognition of capital instruments that no longer qualify as capital	0.00%	[1]
Phase-in of deductions from capital	100.00%	[1]
March 2022 | Common Equity Tier 1 Capital	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	4.50%	[1]
March 2022 | Tier I	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Minimum total capital	6.00%	[1]
March 2022 | G-SIB	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Additional loss absorbency requirements for G-SIBs	'Additional loss absorption capacity tailored to the impact of the entity's default, ranging from 1% to 2.5% of risk-weighted assets, to be met with Common Equity Tier 1 capital
[1]	While these measures are included in the revisions to capital adequacy guidelines that have been applied from March 31, 2013 as published by the Financial Services Agency, capital adequacy guidelines related to other requirements under the Basel III rules, such as the capital conservation buffer, countercyclical buffer and additional loss absorbency requirements for G-SIBs/G-SIFIs, have not yet been published.

Capital_Adequacy_Ratios_of_MHF

Capital Adequacy Ratios of MHFG MHBK and MHTB (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
Total risk-based capital:	'		'
Actual	¥ 2,254,973,000,000		'
Common Equity Tier 1 capital:	'		'
Required	4.50%		'
Total risk-based capital:	'		'
Required	120.00%		'
Consolidated | Mizuho Financial Group Inc	'		'
Common Equity Tier 1 capital:	'		'
Required	2,411,000,000,000		2,059,000,000,000
Actual	5,304,000,000,000		4,804,000,000,000
Tier 1 capital:	'		'
Required	3,316,000,000,000		2,647,000,000,000
Actual	6,845,000,000,000		6,487,000,000,000
Total risk-based capital:	'		'
Required	4,823,000,000,000		4,706,000,000,000
Actual	8,656,000,000,000		8,345,000,000,000
Common Equity Tier 1 capital:	'		'
Required	4.00%		3.50%
Actual	8.79%		8.16%
Tier 1 capital:	'		'
Required	5.50%		4.50%
Actual	11.35%		11.02%
Total risk-based capital:	'		'
Required	8.00%		8.00%
Actual	14.35%		14.18%
Consolidated | Mizuho Bank Limited	'		'
Common Equity Tier 1 capital:	'		'
Required	2,130,000,000,000	[1]	'
Actual	5,387,000,000,000	[1]	'
Tier 1 capital:	'		'
Required	2,928,000,000,000	[1]	'
Actual	6,525,000,000,000	[1]	'
Total risk-based capital:	'		'
Required	4,259,000,000,000	[1]	'
Actual	8,180,000,000,000	[1]	'
Common Equity Tier 1 capital:	'		'
Required	4.00%	[1]	'
Actual	10.11%	[1]	'
Tier 1 capital:	'		'
Required	5.50%	[1]	'
Actual	12.25%	[1]	'
Total risk-based capital:	'		'
Required	8.00%	[1]	'
Actual	15.36%	[1]	'
Consolidated | Mizuho Trust & Banking Company Limited	'		'
Common Equity Tier 1 capital:	'		'
Required	103,000,000,000		91,000,000,000
Actual	379,000,000,000		344,000,000,000
Tier 1 capital:	'		'
Required	141,000,000,000		117,000,000,000
Actual	379,000,000,000		344,000,000,000
Total risk-based capital:	'		'
Required	205,000,000,000		208,000,000,000
Actual	457,000,000,000		448,000,000,000
Common Equity Tier 1 capital:	'		'
Required	4.00%		3.50%
Actual	14.76%		13.24%
Tier 1 capital:	'		'
Required	5.50%		4.50%
Actual	14.76%		13.24%
Total risk-based capital:	'		'
Required	8.00%		8.00%
Actual	17.80%		17.21%
Non-consolidated | Mizuho Bank Limited	'		'
Common Equity Tier 1 capital:	'		'
Required	2,072,000,000,000	[1]	'
Actual	5,260,000,000,000	[1]	'
Tier 1 capital:	'		'
Required	2,849,000,000,000	[1]	'
Actual	6,370,000,000,000	[1]	'
Total risk-based capital:	'		'
Required	4,144,000,000,000	[1]	'
Actual	8,072,000,000,000	[1]	'
Common Equity Tier 1 capital:	'		'
Required	4.00%	[1]	'
Actual	10.15%	[1]	'
Tier 1 capital:	'		'
Required	5.50%	[1]	'
Actual	12.29%	[1]	'
Total risk-based capital:	'		'
Required	8.00%	[1]	'
Actual	15.58%	[1]	'
Non-consolidated | Mizuho Trust & Banking Company Limited	'		'
Common Equity Tier 1 capital:	'		'
Required	101,000,000,000		90,000,000,000
Actual	375,000,000,000		345,000,000,000
Tier 1 capital:	'		'
Required	139,000,000,000		115,000,000,000
Actual	375,000,000,000		345,000,000,000
Total risk-based capital:	'		'
Required	203,000,000,000		205,000,000,000
Actual	¥ 451,000,000,000		¥ 446,000,000,000
Common Equity Tier 1 capital:	'		'
Required	4.00%		3.50%
Actual	14.76%		13.45%
Tier 1 capital:	'		'
Required	5.50%		4.50%
Actual	14.76%		13.45%
Total risk-based capital:	'		'
Required	8.00%		8.00%
Actual	17.79%		17.43%
[1]	The former MHBK and the former MHCB merged on July 1, 2013 and the former MHCB, the surviving company, changed its trade name to MHBK.

Capital_Adequacy_Ratios_of_For

Capital Adequacy Ratios of Former MHCB and Former MHBK (Detail) (JPY ¥)

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2013

Mizuho Corporate Bank Limited

Mizuho Corporate Bank Limited

Mizuho Bank Limited

Mizuho Bank Limited

Mizuho Bank Limited

Mizuho Bank Limited

Former Subsidiary

Former Subsidiary

Consolidated

Non-consolidated

Former Subsidiary

Former Subsidiary

Consolidated

Non-consolidated

Consolidated

Non-consolidated

Common Equity Tier 1 capital:

'

'

'

'

'

'

'

Required

'

¥ 1,292,000,000,000

[1]

¥ 1,143,000,000,000

[1]

¥ 2,130,000,000,000

[2]

¥ 2,072,000,000,000

[2]

¥ 810,000,000,000

[3],[4]

¥ 793,000,000,000

[3],[4]

Actual

'

3,195,000,000,000

[1]

2,993,000,000,000

[1]

5,387,000,000,000

[2]

5,260,000,000,000

[2]

2,061,000,000,000

[3],[4]

2,009,000,000,000

[3],[4]

Tier 1 capital:

'

'

'

'

'

'

'

Required

'

1,661,000,000,000

[1]

1,470,000,000,000

[1]

2,928,000,000,000

[2]

2,849,000,000,000

[2]

1,041,000,000,000

[3],[4]

1,020,000,000,000

[3],[4]

Actual

'

4,071,000,000,000

[1]

3,980,000,000,000

[1]

6,525,000,000,000

[2]

6,370,000,000,000

[2]

2,344,000,000,000

[3],[4]

2,252,000,000,000

[3],[4]

Total risk-based capital:

'

'

'

'

'

'

'

Required

'

2,953,000,000,000

[1]

2,613,000,000,000

[1]

4,259,000,000,000

[2]

4,144,000,000,000

[2]

1,850,000,000,000

[3],[4]

1,813,000,000,000

[3],[4]

Actual

¥ 2,254,973,000,000

¥ 5,130,000,000,000

[1]

¥ 5,008,000,000,000

[1]

¥ 8,180,000,000,000

[2]

¥ 8,072,000,000,000

[2]

¥ 3,259,000,000,000

[3],[4]

¥ 3,163,000,000,000

[3],[4]

Common Equity Tier 1 capital:

'

'

'

'

'

'

'

Required

4.50%

3.50%

[1]

3.50%

[1]

4.00%

[2]

4.00%

[2]

3.50%

[3],[4]

3.50%

[3],[4]

Actual

'

8.65%

[1]

9.16%

[1]

10.11%

[2]

10.15%

[2]

8.90%

[3],[4]

8.86%

[3],[4]

Tier 1 capital:

'

'

'

'

'

'

'

Required

'

4.50%

[1]

4.50%

[1]

5.50%

[2]

5.50%

[2]

4.50%

[3],[4]

4.50%

[3],[4]

Actual

'

11.03%

[1]

12.18%

[1]

12.25%

[2]

12.29%

[2]

10.13%

[3],[4]

9.93%

[3],[4]

Total risk-based capital:

'

'

'

'

'

'

'

Required

120.00%

8.00%

[1]

8.00%

[1]

8.00%

[2]

8.00%

[2]

8.00%

[3],[4]

8.00%

[3],[4]

Actual

'

13.89%

[1]

15.33%

[1]

15.36%

[2]

15.58%

[2]

14.08%

[3],[4]

13.95%

[3],[4]

[1]

The distribution of all of the shares of MHSC to MHFG as a dividend in kind (¥424.4 billion) on April 1, 2013 was deducted from Common Equity Tier 1 capital.

[2]

The former MHBK and the former MHCB merged on July 1, 2013 and the former MHCB, the surviving company, changed its trade name to MHBK.

[3]

The amounts and ratios were calculated in accordance with Basel III and are included for reference purpose only because the former MHBK was subject to Basel II requirements as of March 31, 2013 as a financial institution without overseas operations to which only domestic capital adequacy requirements applied.

[4]

The distribution of all of the shares of MHSC to MHFG as a dividend in kind (¥125.7 billion) on April 1, 2013 was deducted from Common Equity Tier 1 capital.

Capital_Adequacy_Ratios_of_For1

Capital Adequacy Ratios of Former MHCB and Former MHBK (Parenthetical) (Detail) (JPY ¥)	1 Months Ended
In Billions, unless otherwise specified	Apr. 30, 2013
Mizuho Corporate Bank Limited	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Dividend payment	¥ 424.4
Mizuho Bank Limited	'
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]	'
Dividend payment	¥ 125.7

Computation_of_Basic_and_Dilut

Computation of Basic and Diluted Earnings Per Common Share (Detail) (JPY ¥)	12 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Net income:	'		'		'
Net income attributable to MHFG shareholders	¥ 498,484		¥ 875,412		¥ 656,389
Less: Net income attributable to preferred shareholders	6,745		8,221		8,672
Net income attributable to common shareholders	491,739		867,191		647,717
Effect of dilutive securities:	'		'		'
Convertible preferred stock	6,437		7,121		7,571
Net income attributable to common shareholders after assumed conversions	¥ 498,176		¥ 874,312		¥ 655,288
Shares:	'		'		'
Weighted average common shares outstanding	24,189,670		24,053,282		23,073,544
Effect of dilutive securities:	'		'		'
Convertible preferred stock	1,164,941	[1]	1,291,854	[1]	1,384,367	[1]
Stock compensation-type stock options	16,641		20,093		11,628
Weighted average common shares after assumed conversions	25,371,252		25,365,229		24,469,539
Amounts per common share:	'		'		'
Basic net income per common share	¥ 20.33		¥ 36.05		¥ 28.07
Diluted net income per common share	¥ 19.64		¥ 34.47		¥ 26.78
[1]	The number of the dilutive common shares is based on the applicable conversion prices.

Components_of_Income_Tax_Expen

Components of Income Tax Expense (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Current:	'	'	'
Domestic	¥ 92,814	¥ 37,101	¥ 22,103
Foreign	42,919	10,754	32,714
Total current tax expense	135,733	47,855	54,817
Deferred:	'	'	'
Domestic	94,911	-40,021	-36,777
Foreign	-4,536	-3,810	-4,162
Total deferred tax expense	90,375	-43,831	-40,939
Income tax expense (benefit)	¥ 226,108	¥ 4,024	¥ 13,878

Tax_Effects_of_Items_Recorded_

Tax Effects of Items Recorded Directly in Equity (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Unrealized net gains (losses) on available-for-sale securities:	'	'	'
Unrealized gains (losses)	¥ 161,269	¥ 235,274	¥ 29,925
Less: reclassification adjustments	-70,228	-33,988	18,249
Total	91,041	201,286	48,174
Pension liability adjustments:	'	'	'
Unrealized gains (losses)	71,646	34,171	2,367
Less: reclassification adjustments	2,442	5,913	8,992
Total	74,088	40,084	11,359
Total tax effect before allocation to noncontrolling interests	¥ 165,129	¥ 241,370	¥ 59,533

Reconciliation_of_Income_Tax_E

Reconciliation of Income Tax Expense at Effective Statutory Tax Rate to Actual Income Tax Expense (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013	Mar. 31, 2012
Reconciliation of Statutory Federal Tax Rate [Line Items]	'		'	'
Income before income tax expense (benefit)	¥ 726,343		¥ 885,180	¥ 662,835
Effective statutory tax rate	38.01%		38.01%	40.69%
Income tax calculated at the statutory tax rate	276,083		336,457	269,708
Income not subject to tax	-22,354		-18,320	-18,295
Expenses not deductible for tax purposes	1,550		1,348	1,469
Tax rate differentials of subsidiaries	-1,611		-10,535	-4,142
Change in valuation allowance	-50,933		-1,352,597	-371,271
Change in undistributed earnings of subsidiaries	932		12,233	-7,118
Change in net operating loss carryforwards resulting from intercompany capital transactions	235		227	162
Expiration of net operating loss carryforwards	6,313		1,026,439	33,576
Effect of enacted change in tax rates	15,786	[1]	'	107,011	[2]
Other	107		8,772	2,778
Income tax expense (benefit)	¥ 226,108		¥ 4,024	¥ 13,878
[1]	On March 20, 2014, the National Diet of Japan approved a bill affecting the statutory tax rates of MHFG and its domestic subsidiaries. As a result, the statutory tax rate concerning MHFG's tax returns for the fiscal year ending March 31, 2015 will be reduced to 35.64% from the previous rate of 38.01%. The decrease of the Group's balance of net deferred tax assets, reflecting such tax rate reductions, was recognized in Income tax expense in the fiscal year ended March 31, 2014.
[2]	On November 30, 2011, the National Diet of Japan approved two bills affecting the statutory tax rates of MHFG and its domestic subsidiaries. As a result, the statutory tax rate concerning MHFG's tax returns for the fiscal years ended March 31, 2013 and 2014 has been reduced to 38.01% from the previous rate of 40.69%. Also, the rates for the fiscal year ending March 31, 2015 and for the fiscal years ending March 31, 2016 and thereafter will be 38.01% and 35.64%, respectively. The decrease of the Group's balance of net deferred tax assets, reflecting such tax rate reductions, was recognized in Income tax expense in the fiscal year ended March 31, 2012.

Reconciliation_of_Income_Tax_E1

Reconciliation of Income Tax Expense at Effective Statutory Tax Rate to Actual Income Tax Expense (Parenthetical) (Detail)	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Reconciliation of Statutory Federal Tax Rate [Line Items]	'	'	'
Effective statutory tax rate	38.01%	38.01%	40.69%
31-Mar-15	'	'	'
Reconciliation of Statutory Federal Tax Rate [Line Items]	'	'	'
Effective statutory tax rate	35.64%	38.01%	'
March 31, 2016 and thereafter	'	'	'
Reconciliation of Statutory Federal Tax Rate [Line Items]	'	'	'
Effective statutory tax rate	'	35.64%	'

Components_of_Net_Deferred_Tax

Components of Net Deferred Tax Assets (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Millions, unless otherwise specified
Deferred tax assets:	'	'
Investments	¥ 724,038	¥ 889,305
Allowance for loan losses	266,595	337,453
Derivative financial instruments	29,002	'
Trading account assets	19,842	'
Net operating loss carryforwards	448,926	450,016
Other	204,304	264,661
Deferred Tax Assets, Gross, Total	1,692,707	1,941,435
Valuation allowance	-443,847	-584,665
Deferred tax assets, net of valuation allowance	1,248,860	1,356,770
Deferred tax liabilities:	'	'
Available-for-sale securities	659,448	567,608
Prepaid pension cost and accrued pension liabilities	132,738	39,937
Undistributed earnings of subsidiaries	11,972	11,040
Premises and equipment	11,263	12,304
Derivative financial instruments	'	35,391
Trading account assets	'	11,101
Other	61,500	51,913
Deferred tax liabilities	876,921	729,294
Net deferred tax assets	¥ 371,939	¥ 627,476

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014
					Japan	United States	United Kingdom	Parent Company
Income Taxes [Line Items]	'	'	'	'	'	'	'	'
Net operating loss carryforwards	¥ 1,414,000,000,000	'	'	'	'	'	'	¥ 868,000,000,000
Unrecognized tax benefits, interest and penalties	699,000,000	563,000,000	802,000,000	'	'	'	'	'
Unrecognized tax benefits	¥ 1,691,000,000	¥ 1,454,000,000	¥ 2,160,000,000	¥ 1,829,000,000	'	'	'	'
Open tax year	'	'	'	'	'2006	'2002	'2002	'

Net_Operating_Losses_Carryforw

Net Operating Losses Carryforwards by Expiration Date (Detail) (JPY ¥)	Mar. 31, 2014
In Billions, unless otherwise specified
Operating Loss Carryforwards [Line Items]	'
Net operating loss carryforwards	¥ 1,414
2018	'
Operating Loss Carryforwards [Line Items]	'
Net operating loss carryforwards	865
2019	'
Operating Loss Carryforwards [Line Items]	'
Net operating loss carryforwards	8
2020 and thereafter	'
Operating Loss Carryforwards [Line Items]	'
Net operating loss carryforwards	¥ 541

RollForward_of_Unrecognized_Ta

Roll-Forward of Unrecognized Tax Benefits (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Income Tax Contingency [Line Items]	'	'	'
Total unrecognized tax benefits at beginning of fiscal year	¥ 1,454	¥ 2,160	¥ 1,829
Gross amount of increases (decreases) related to positions taken during prior years	-6	-471	362
Gross amount of increases related to positions taken during the current year	100	29	244
Amount of decreases related to settlements	'	-559	-227
Foreign exchange translation	143	295	-48
Total unrecognized tax benefits at end of fiscal year	¥ 1,691	¥ 1,454	¥ 2,160

Recovered_Sheet4

Pension and Other Employee Benefit Plans - Additional Information (Detail) (JPY ¥)	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Defined contribution plans, costs recognized in respect of contributions to the plans	¥ 2,487,000,000	¥ 1,968,000,000	¥ 2,129,000,000
Amounts in accumulated other comprehensive income (loss) expected to be amortized as prior service cost or benefit over the next fiscal year	195,000,000	'	'
Amounts in accumulated other comprehensive income (loss) expected to be amortized as actuarial loss over the next fiscal year	137,000,000	'	'
Total benefit obligations of group, decrease	-110,744,000,000	'	'
Pension plan, contribution expected to be paid during the next fiscal year	¥ 49,000,000,000	'	'

Net_Periodic_Benefit_Cost_of_S

Net Periodic Benefit Cost of Severance Indemnities and Pension Plans (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost-benefits earned during the fiscal year	¥ 33,429	¥ 30,422	¥ 27,734
Interest costs on projected benefit obligation	20,341	23,186	24,267
Expected return on plan assets	-37,047	-32,237	-28,234
Amortization of prior service benefit	-195	-319	-318
Amortization of net actuarial loss (gain)	7,039	16,936	25,595
Special termination benefits	5,429	5,454	14,115	[1]
Net periodic benefit cost	¥ 28,996	¥ 43,442	¥ 63,159
[1]	The amount for the fiscal year ended March 31, 2012 includes special termination benefits of ¥9,828 million pertaining to MHSC's voluntary retirement scheme.

Net_Periodic_Benefit_Cost_of_S1

Net Periodic Benefit Cost of Severance Indemnities and Pension Plans (Parenthetical) (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Special termination benefits	¥ (5,429)	¥ (5,454)	¥ (14,115)	[1]
Voluntary retirement scheme	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Special termination benefits	'	'	¥ 9,828
[1]	The amount for the fiscal year ended March 31, 2012 includes special termination benefits of ¥9,828 million pertaining to MHSC's voluntary retirement scheme.

Other_Changes_in_Plan_Assets_a

Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) Before-Tax (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Plan Disclosure [Line Items]	'	'
Net actuarial gain (loss)	¥ 204,506	¥ 103,683
Amortization of net actuarial loss (gain)	7,039	16,936
Prior service benefit (cost)	'	-1,782
Amortization of prior service benefit	-195	-319
Total recognized in other comprehensive income (loss) before-tax	¥ 211,350	¥ 118,518

WeightedAverage_Assumptions_Us

Weighted-Average Assumptions Used to Determine Benefit Obligations and Net Periodic Benefit Cost (Detail)	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Weighted-average assumptions used to determine benefit obligations at fiscal year end:	'	'	'
Discount rates	0.96%	1.44%	1.73%
Weighted-average assumptions used to determine net periodic benefit cost during the year:	'	'	'
Discount rates	1.44%	1.73%	1.83%
Expected rates of return on plan assets	2.42%	2.40%	2.27%
Minimum	'	'	'
Weighted-average assumptions used to determine benefit obligations at fiscal year end:	'	'	'
Rates of increase in future compensation levels	2.00%	2.31%	2.33%
Weighted-average assumptions used to determine net periodic benefit cost during the year:	'	'	'
Rates of increase in future compensation levels	2.31%	2.33%	2.28%
Maximum	'	'	'
Weighted-average assumptions used to determine benefit obligations at fiscal year end:	'	'	'
Rates of increase in future compensation levels	4.80%	6.57%	6.46%
Weighted-average assumptions used to determine net periodic benefit cost during the year:	'	'	'
Rates of increase in future compensation levels	6.57%	6.46%	6.15%

Combined_Funded_Status_and_Amo

Combined Funded Status and Amounts Recognized in Accompanying Consolidated Balance Sheets (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Change in benefit obligation:	'		'		'
Benefit obligation at beginning of fiscal year	¥ 1,399,123	[1]	¥ 1,343,714		'
Service cost	33,429		30,422		27,734
Interest cost	20,341		23,186		24,267
Plan participants' contributions	1,181		1,184		'
Amendments	'		1,782		'
Actuarial loss (gain)	-70,214		63,140		'
Foreign exchange translation	4,854		2,209		'
Benefits paid	-49,905		-49,593		'
Lump-sum payments	-18,119		-16,921		'
Benefit obligation at end of fiscal year	1,320,690	[1]	1,399,123	[1]	1,343,714
Change in plan assets:	'		'		'
Fair value of plan assets at beginning of fiscal year	1,527,744		1,323,163		'
Actual return (negative return) on plan assets	171,970		199,341		'
Foreign exchange translation	4,128		1,783		'
Employer contributions	50,936		51,866		'
Plan participants' contributions	1,181		1,184		'
Benefits paid	-49,905		-49,593		'
Fair value of plan assets at end of fiscal year	1,706,054		1,527,744		1,323,163
Funded status	385,364		128,621		'
Amounts recognized in the consolidated balance sheets consist of:	'		'		'
Prepaid pension cost	403,654		153,414		'
Accrued pension liability	-18,290		-24,793		'
Net amount recognized	385,364		128,621		'
Amounts recognized in Accumulated other comprehensive income (loss) before-tax consist of:	'		'		'
Prior service benefit (cost)	-635		-440		'
Net actuarial gain (loss)	-24,814		-236,359		'
Net amount recognized	¥ (25,449)		¥ (236,799)		'
[1]	The aggregated accumulated benefit obligations of these plans were ¥1,364,786 million and ¥1,319,771 million, respectively, as of March 31, 2013 and 2014. The defined benefit plans generally employ a multi-variable and non-linear formula based upon rank and years of service. Employees with service in excess of one year are qualified to receive lump-sum severance indemnities.

Combined_Funded_Status_and_Amo1

Combined Funded Status and Amounts Recognized in Accompanying Consolidated Balance Sheets (Parenthetical) (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Plan Disclosure [Line Items]	'	'
Aggregated accumulated benefit obligations	¥ 1,319,771	¥ 1,364,786
Description of requirements for lump-sum severance indemnities	'Employees with service in excess of one year are qualified to receive lump-sum severance indemnities.	'

Plans_with_Projected_Benefit_O

Plans with Projected Benefit Obligations in Excess of Plan Assets and Plans with Accumulated Benefit Obligations in Excess of Plan Assets (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Millions, unless otherwise specified
Plans with projected benefit obligations in excess of plan assets:	'		'
Projected benefit obligation	¥ 40,509	[1]	¥ 95,789	[1]
Fair value of plan assets	21,898		70,690
Plans with accumulated benefit obligations in excess of plan assets:	'		'
Accumulated benefit obligation	39,590		91,210
Fair value of plan assets	¥ 21,898		¥ 70,690
[1]	The plans with projected benefit obligations in excess of plan assets include those with accumulated benefit obligations in excess of plan assets.

Target_Allocation_for_Plan_Ass

Target Allocation for Plan Assets Excluding those of Employee Retirement Benefit Trusts (Detail)	12 Months Ended
	Mar. 31, 2014
Asset category	'
Plan assets	100.00%
General Account Assets	'
Asset category	'
Plan assets	14.00%	[1]
Other assets	'
Asset category	'
Plan assets	1.00%
Japan | Equity securities	'
Asset category	'
Plan assets	5.00%
Japan | Debt securities	'
Asset category	'
Plan assets	44.00%
Foreign | Equity securities	'
Asset category	'
Plan assets	26.00%
Foreign | Debt securities	'
Asset category	'
Plan assets	10.00%
[1]	General account of life insurance companies is a contract with life insurance companies which guarantees payments of principal and predetermined interest rate.

Fair_Value_of_Plan_Assets_by_A

Fair Value of Plan Assets by Asset Category (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
In Millions, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	¥ 1,706,054		¥ 1,527,744		¥ 1,323,163
General account of life insurance companies	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	111,000	[1]	111,000	[1]	'
Hedge funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	2,000		1,000		'
Other Invested Assets	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	88,000		90,000		'
Japan | Equity securities | Common stocks	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	782,000	[2]	716,000	[2]	'
Japan | Equity securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	56,000	[3]	86,000	[3]	'
Japan | Debt securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	68,000	[3]	46,000	[3]	'
Japan | Debt securities | Government bonds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	229,000		179,000		'
Japan | Debt securities | Other	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	24,000		7,000		'
Foreign | Equity securities | Common stocks	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	99,000		56,000		'
Foreign | Equity securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	154,000	[3]	92,000	[3]	'
Foreign | Debt securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	9,000	[3]	46,000	[3]	'
Foreign | Debt securities | Government bonds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	69,000		75,000		'
Foreign | Debt securities | Other	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	15,000		23,000		'
Level 1	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	1,281,000		1,112,000		'
Level 1 | Other Invested Assets	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	91,000	[4]	92,000	[4]	'
Level 1 | Japan | Equity securities | Common stocks	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	782,000	[2]	716,000	[2]	'
Level 1 | Japan | Equity securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	5,000	[3]	'		'
Level 1 | Japan | Debt securities | Government bonds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	229,000		179,000		'
Level 1 | Foreign | Equity securities | Common stocks	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	96,000		54,000		'
Level 1 | Foreign | Equity securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	15,000	[3]	'		'
Level 1 | Foreign | Debt securities | Government bonds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	63,000		71,000		'
Level 2	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	423,000		415,000		'
Level 2 | General account of life insurance companies	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	111,000	[1]	111,000	[1]	'
Level 2 | Other Invested Assets	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	-3,000	[5]	-2,000	[5]	'
Level 2 | Japan | Equity securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	51,000	[3]	86,000	[3]	'
Level 2 | Japan | Debt securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	68,000	[3]	46,000	[3]	'
Level 2 | Japan | Debt securities | Other	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	24,000		7,000		'
Level 2 | Foreign | Equity securities | Common stocks	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	3,000		2,000		'
Level 2 | Foreign | Equity securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	139,000	[3]	92,000	[3]	'
Level 2 | Foreign | Debt securities | Pooled funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	9,000	[3]	46,000	[3]	'
Level 2 | Foreign | Debt securities | Government bonds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	6,000		4,000		'
Level 2 | Foreign | Debt securities | Other	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	15,000		23,000		'
Level 3	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	2,000		1,000		'
Level 3 | Hedge funds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair values of plan assets	¥ 2,000		¥ 1,000		'
[1]	Investments in this class are measured at conversion value.
[2]	This class includes equity securities held in the employee retirement benefit trusts of ¥681 billion and ¥782 billion at March 31, 2013 and 2014, respectively, which are well-diversified across industries.
[3]	These classes primarily include pension investment fund trusts. Investments in these classes are generally measured at their net asset values per share and can be redeemable within a short-term period upon request.
[4]	Amounts primarily include cash and short-term assets carried at fair value.
[5]	Amounts primarily include foreign exchange contracts carried at fair value.

Fair_Value_of_Plan_Assets_by_A1

Fair Value of Plan Assets by Asset Category (Parenthetical) (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
In Millions, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Equity securities held in the employee retirement benefit trusts	¥ 1,706,054		¥ 1,527,744		¥ 1,323,163
Equity securities | Common stocks | Japan	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Equity securities held in the employee retirement benefit trusts	782,000	[1]	716,000	[1]	'
Equity securities | Trust for Benefit of Employees | Common stocks | Japan	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Equity securities held in the employee retirement benefit trusts	¥ 782,000		¥ 681,000		'
[1]	This class includes equity securities held in the employee retirement benefit trusts of ¥681 billion and ¥782 billion at March 31, 2013 and 2014, respectively, which are well-diversified across industries.

Forecasted_Benefit_Payments_In

Forecasted Benefit Payments Including Effect of Expected Future Service (Detail) (JPY ¥)	Mar. 31, 2014
In Millions, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]	'
2015	¥ 65,570
2016	68,183
2017	70,083
2018	71,558
2019	72,543
2020-2024	¥ 355,295

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (JPY ¥)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Number of types of stock-based compensation plans	1	'	'
Stock-based compensation plan, shares of common stock to be issued or transferred upon exercise of each of the stock acquisition rights	1,000	'	'
Stock-based compensation plan, exercise price per share	¥ 1	'	'
Stock-based compensation plan, contractual term (in years)	'20 years	'	'
Mizuho Financial Group Inc, Mizuho Bank Limited and Mizuho Corporate Bank Limited	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Stock-based compensation plan, exercise price per share	¥ 1	'	'
Stock-based compensation plan, weighted-average grant-date fair value	¥ 192,610	¥ 113,250	¥ 91,840
Stock-based compensation plan, compensation cost recognized in income	¥ 1,527	¥ 1,333	¥ 788

Summary_of_StockBased_Compensa

Summary of Stock-Based Compensation Plan (Detail) (JPY ¥)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2014
Weighted-average exercise price	'
Exercisable at end of fiscal year	¥ 1
Mizuho Financial Group Inc, Mizuho Bank Limited and Mizuho Corporate Bank Limited	'
Number of shares	'
Outstanding at beginning of fiscal year	23,863,000
Granted during fiscal year	7,932,000
Exercised during fiscal year	9,252,000
Outstanding at end of fiscal year	22,543,000
Exercisable at end of fiscal year	630,000
Weighted-average exercise price	'
Outstanding at beginning of fiscal year	¥ 1
Granted during fiscal year	¥ 1
Exercised during fiscal year	¥ 1
Outstanding at end of fiscal year	¥ 1
Exercisable at end of fiscal year	¥ 1
Weighted-average remaining contractual term	'
Outstanding at end of fiscal year	'18 years 5 months 19 days
Exercisable at end of fiscal year	'16 years 3 months 22 days
Aggregate intrinsic value	'
Outstanding at end of fiscal year	¥ 4,576
Exercisable at end of fiscal year	¥ 128

Assumptions_to_Estimate_Fair_V

Assumptions to Estimate Fair Value of Stock Acquisition Rights on Date of Grant Used in Black-Scholes Option Pricing Model (Detail) (Mizuho Financial Group Inc, Mizuho Bank Limited and Mizuho Corporate Bank Limited)	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Mizuho Financial Group Inc, Mizuho Bank Limited and Mizuho Corporate Bank Limited	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Risk-free interest rate	0.08%	0.10%
Expected volatility	28.16%	29.30%
Expected remaining term (in years)	'2 years 5 months 16 days	'2 years 5 months 1 day
Expected dividend yield	3.11%	4.69%

Notional_and_Fair_Value_Amount

Notional and Fair Value Amounts of Derivative Instruments Outstanding (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Billions, unless otherwise specified
Derivatives, Fair Value [Line Items]	'		'
Notional amount	¥ 1,099,907	[1]	¥ 982,613	[1]
Interest rate contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Notional amount	971,939	[1]	854,698	[1]
Foreign exchange contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Notional amount	119,864	[1]	118,708	[1]
Equity-related contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Notional amount	2,979	[1]	3,419	[1]
Credit-related contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Notional amount	4,662	[1]	5,266	[1]
Other contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Notional amount	463	[1]	522	[1]
Designated as Hedging Instrument	'		'
Derivatives, Fair Value [Line Items]	'		'
Fair value of derivative receivables	1	[2]	'
Fair value of derivative payables	2	[2]	10	[2]
Designated as Hedging Instrument | Foreign exchange contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Fair value of derivative payables	2	[2]	10	[2]
Designated as Hedging Instrument | Equity-related contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Fair value of derivative receivables	1	[2]	'
Not Designated as Hedging Instrument	'		'
Derivatives, Fair Value [Line Items]	'		'
Fair value of derivative receivables	10,686	[2]	13,728	[2]
Fair value of derivative payables	10,473	[2]	13,239	[2]
Not Designated as Hedging Instrument | Interest rate contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Fair value of derivative receivables	8,064	[2]	10,350	[2]
Fair value of derivative payables	7,895	[2]	10,018	[2]
Not Designated as Hedging Instrument | Foreign exchange contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Fair value of derivative receivables	2,354	[2]	3,099	[2]
Fair value of derivative payables	2,349	[2]	2,973	[2]
Not Designated as Hedging Instrument | Equity-related contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Fair value of derivative receivables	196	[2]	182	[2]
Fair value of derivative payables	178	[2]	177	[2]
Not Designated as Hedging Instrument | Credit-related contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Fair value of derivative receivables	49	[2]	59	[2]
Fair value of derivative payables	34	[2]	44	[2]
Not Designated as Hedging Instrument | Other contracts	'		'
Derivatives, Fair Value [Line Items]	'		'
Fair value of derivative receivables	23	[2]	38	[2]
Fair value of derivative payables	¥ 17	[2]	¥ 27	[2]
[1]	Notional amount represents the sum of gross long and gross short third-party contracts.
[2]	Derivative receivables and payables are recorded in Trading account assets and Trading account liabilities, respectively.

Recovered_Sheet5

Derivative Financial Instruments - Additional Information (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
Derivative [Line Items]	'	'
Cash collateral provided and not offset against derivative positions and included in Other assets	¥ 466,420,000,000	¥ 742,307,000,000
Cash collateral accepted and not offset against derivative positions and included in Other liabilities	432,820,000,000	503,101,000,000
Aggregate fair value of derivative instruments with credit-risk-related contingent features in liability positions	687,000,000,000	1,022,000,000,000
Collateral provided to counterparties in normal course of business	614,000,000,000	1,029,000,000,000
Amount immediately required to settle if credit-risk-related contingent features were triggered	¥ 73,000,000,000	¥ 0

Gains_and_Losses_Information_R

Gains and Losses Information Related to Fair Value Hedges (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'
Gains (losses) recorded in income- Derivatives	¥ 801	¥ 396	¥ (499)
Gains (losses) recorded in income- Hedged items	-1,112	-475	428
Gains (losses) recorded in income- Hedge ineffectiveness	'	'	'
Gains (losses) recorded in income- Net gain (loss) excluded from assessment of effectiveness	-311	-79	-71
Interest rate contracts	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'
Gains (losses) recorded in income- Derivatives	'	44	-214
Gains (losses) recorded in income- Hedged items	'	-81	150
Gains (losses) recorded in income- Hedge ineffectiveness	'	'	'
Gains (losses) recorded in income- Net gain (loss) excluded from assessment of effectiveness	'	-37	-64
Equity-related contracts	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'
Gains (losses) recorded in income- Derivatives	801	352	-285
Gains (losses) recorded in income- Hedged items	-1,112	-394	278
Gains (losses) recorded in income- Hedge ineffectiveness	'	'	'
Gains (losses) recorded in income- Net gain (loss) excluded from assessment of effectiveness	¥ (311)	¥ (42)	¥ (7)

Gains_and_Losses_Information_R1

Gains and Losses Information Related to Net Investment Hedges (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'
Effective portion recorded in OCI	¥ (102,150)	¥ (65,851)	¥ 8,024
Ineffective portion recorded in income	-7,316	-2,908	1,666
Financial instruments hedging foreign exchange risk	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'
Effective portion recorded in OCI	-102,150	-65,851	8,024
Ineffective portion recorded in income	¥ (7,316)	¥ (2,908)	¥ 1,666

Gains_and_Losses_Information_R2

Gains and Losses Information Related to Net Investment Hedges (Parenthetical) (Detail) (Financial instruments hedging foreign exchange risk, JPY ¥)	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
In Millions, unless otherwise specified
Financial instruments hedging foreign exchange risk	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'
Accumulated other comprehensive income (loss) reclassified to earnings	¥ 0	¥ 13,858	¥ 1,893

Gains_and_Losses_on_Derivative

Gains and Losses on Derivatives Not Designated or Qualifying as Hedges (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gains (losses) recorded in income	¥ (148,643)		¥ 59,446		¥ 102,939
Interest rate contracts	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gains (losses) recorded in income	-79,562	[1]	219,422	[1]	261,632	[1]
Foreign exchange contracts	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gains (losses) recorded in income	-13,167		-91,300		-146,258
Equity-related contracts	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gains (losses) recorded in income	-41,296	[1]	-59,421	[1]	-7,143	[1]
Credit-related contracts	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gains (losses) recorded in income	-7,761	[2]	-6,877	[2]	-5,575	[2]
Other contracts	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gains (losses) recorded in income	¥ (6,857)		¥ (2,378)		¥ 283
[1]	The net gain (loss) excluded from the assessment of the effectiveness of fair value hedges is not included in the above table.
[2]	Amounts include the net loss of ¥3,391 million, ¥6,703 million and ¥8,660 million on the credit derivatives hedging the credit risk of loans during the fiscal years ended March 31, 2012, 2013 and 2014, respectively.

Gains_and_Losses_on_Derivative1

Gains and Losses on Derivatives Not Designated or Qualifying as Hedges (Parenthetical) (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gains (losses) recorded in income	¥ (148,643)		¥ 59,446		¥ 102,939
Credit-related contracts	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gains (losses) recorded in income	-7,761	[1]	-6,877	[1]	-5,575	[1]
Loans related to credit derivatives | Credit-related contracts	'		'		'
Derivative Instruments, Gain (Loss) [Line Items]	'		'		'
Gains (losses) recorded in income	¥ (8,660)		¥ (6,703)		¥ (3,391)
[1]	Amounts include the net loss of ¥3,391 million, ¥6,703 million and ¥8,660 million on the credit derivatives hedging the credit risk of loans during the fiscal years ended March 31, 2012, 2013 and 2014, respectively.

Notional_and_Fair_Value_Amount1

Notional and Fair Value Amounts of Credit Derivatives (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Credit protection written	'	'
Credit Derivatives [Line Items]	'	'
Notional amount	¥ 2,202	¥ 2,462
Fair value	24	2
Credit protection written | Investment grade	'	'
Credit Derivatives [Line Items]	'	'
Notional amount	1,723	1,810
Fair value	21	1
Credit protection written | Non-investment grade	'	'
Credit Derivatives [Line Items]	'	'
Notional amount	479	652
Fair value	3	1
Credit protection purchased	'	'
Credit Derivatives [Line Items]	'	'
Notional amount	2,548	2,870
Fair value	¥ (9)	¥ 13

Maximum_Potential_Amount_of_Fu

Maximum Potential Amount of Future Payments for Credit Protection Written by Expiration Period (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Credit Derivatives [Line Items]	'	'
Maximum payout/Notional amount	¥ 2,202	¥ 2,462
One year or less	'	'
Credit Derivatives [Line Items]	'	'
Maximum payout/Notional amount	325	620
After one year through five years	'	'
Credit Derivatives [Line Items]	'	'
Maximum payout/Notional amount	1,791	1,720
After five years	'	'
Credit Derivatives [Line Items]	'	'
Maximum payout/Notional amount	¥ 86	¥ 122

Recovered_Sheet6

Commitments and Contingencies - Additional Information (Detail) (JPY ¥)	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Commitments and Contingencies Disclosure [Line Items]	'	'	'
Carrying amount of guarantees and similar obligations	¥ 422,000,000,000	¥ 512,000,000,000	'
Carrying amounts of derivatives that are deemed to guarantees	404,000,000,000	493,000,000,000	'
Total rental expense	95,941,000,000	98,459,000,000	101,003,000,000
Sale Leaseback transactions accounted as an operating leases, total rental payment for the whole period in the original contracts	214,690,000,000	'	'
Sale Leaseback transactions accounted as an operating leases, total rental payment for the whole period in the current contracts	282,832,000,000	'	'
Sale Leaseback transactions accounted as an operating leases, future minimum rental payments	69,556,000,000	15,907,000,000	29,879,000,000
Off-balance Sheet instruments	'	'	'
Commitments and Contingencies Disclosure [Line Items]	'	'	'
Allowance for losses on off-balance-sheet instruments	¥ 121,000,000,000	¥ 102,000,000,000	'

Maximum_Exposure_or_Notional_A

Maximum Exposure or Notional Amount Under Guarantee Contracts (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	¥ 3,803	¥ 3,416
Performance guarantees	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	1,985	1,750
Guarantees on loans	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	399	452
Guarantees on securities	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	170	146
Other guarantees	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	1,249	1,068
Guarantees for the repayment of trust principal	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	158	171
Liabilities of trust accounts	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	11,158	8,606
Derivative financial instruments	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	21,422	23,582
One year or less | Performance guarantees	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	1,125	935
One year or less | Guarantees on loans	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	173	159
One year or less | Guarantees on securities	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	42	19
One year or less | Other guarantees	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	991	826
One year or less | Liabilities of trust accounts	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	10,962	8,428
One year or less | Derivative financial instruments	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	8,643	10,185
After one year through five years | Performance guarantees	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	708	619
After one year through five years | Guarantees on loans	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	21	51
After one year through five years | Guarantees on securities	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	128	127
After one year through five years | Other guarantees	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	220	217
After one year through five years | Guarantees for the repayment of trust principal	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	125	133
After one year through five years | Liabilities of trust accounts	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	78	72
After one year through five years | Derivative financial instruments	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	11,391	11,837
After five years | Performance guarantees	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	152	196
After five years | Guarantees on loans	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	205	242
After five years | Other guarantees	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	38	25
After five years | Guarantees for the repayment of trust principal	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	33	38
After five years | Liabilities of trust accounts	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	118	106
After five years | Derivative financial instruments	'	'
Guarantor Obligations [Line Items]	'	'
Maximum potential/Contractual or Notional amount	¥ 1,388	¥ 1,560

Maximum_Potential_Amount_of_Fu1

Maximum Potential Amount of Future Payments of Performance Guarantees Guarantees on Loans Guarantees on Securities and Other Guarantees Classified Based on Internal Ratings (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Billions, unless otherwise specified
Guarantor Obligations [Line Items]	'		'
Maximum potential/Contractual or Notional amount	¥ 3,803		¥ 3,416
Investment grade	'		'
Guarantor Obligations [Line Items]	'		'
Maximum potential/Contractual or Notional amount	2,673	[1]	2,387	[1]
Non-investment grade	'		'
Guarantor Obligations [Line Items]	'		'
Maximum potential/Contractual or Notional amount	¥ 1,130		¥ 1,029
[1]	Investment grade in the internal rating scale generally corresponds to BBB- or above in external rating scale.

Contractual_Amounts_With_Regar

Contractual Amounts With Regard to Undrawn Commitments (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Billions, unless otherwise specified
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]	'		'
Off-balance-sheet instruments, contractual amounts of the undrawn commitments	¥ 60,013		¥ 59,709
Commitments to Extend Credit	'		'
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]	'		'
Off-balance-sheet instruments, contractual amounts of the undrawn commitments	59,402	[1]	59,101	[1]
Commercial letters of credit	'		'
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]	'		'
Off-balance-sheet instruments, contractual amounts of the undrawn commitments	¥ 611		¥ 608
[1]	Commitments to extend credit include commitments to invest in securities.

Future_Minimum_Lease_Payments_

Future Minimum Lease Payments for Capitalized Leases and Rental Payments for Operating Leases (Detail) (JPY ¥)	Mar. 31, 2014
In Millions, unless otherwise specified
Capitalized leases	'
2015	¥ 6,479
2016	5,929
2017	5,186
2018	4,547
2019	3,820
2020 and thereafter	2,068
Total minimum lease/rental payments	28,029
Amount representing interest	1,349
Present value of minimum lease payments	26,680
Operating leases	'
2015	48,233
2016	40,195
2017	35,584
2018	31,556
2019	29,237
2020 and thereafter	74,596
Total minimum lease/rental payments	¥ 259,401

Recovered_Sheet7

Noncontrolling Interests in Consolidated Subsidiaries - Additional Information (Detail)	Mar. 31, 2012
Mizuho Trust & Banking Company Limited	'
Noncontrolling Interest [Line Items]	'
Voting equity interests in subsidiaries	30.15%
The Former Mizuho Securities Company Limited	'
Noncontrolling Interest [Line Items]	'
Voting equity interests in subsidiaries	40.80%
The Former Mizuho Investors Securities Company Limited	'
Noncontrolling Interest [Line Items]	'
Voting equity interests in subsidiaries	46.02%
Bank Subsidiaries	'
Noncontrolling Interest [Line Items]	'
Voting interest transferred	5.34%

Consolidated_Assets_of_Groups_

Consolidated Assets of Groups Consolidated VIEs as well as Total Assets and Maximum Exposure to Loss for Its Significant Unconsolidated VIEs (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Variable Interest Entity [Line Items]	'	'
Consolidated VIEs- Consolidated assets	¥ 4,553	¥ 3,811
Significant unconsolidated VIEs- Total assets	3,851	3,763
Significant unconsolidated VIEs- Maximum exposure to loss	626	545
Asset-backed commercial paper/loan programs	'	'
Variable Interest Entity [Line Items]	'	'
Consolidated VIEs- Consolidated assets	2,403	2,212
Asset-backed securitizations	'	'
Variable Interest Entity [Line Items]	'	'
Consolidated VIEs- Consolidated assets	423	385
Significant unconsolidated VIEs- Total assets	385	463
Significant unconsolidated VIEs- Maximum exposure to loss	39	37
Investments in securitization products	'	'
Variable Interest Entity [Line Items]	'	'
Consolidated VIEs- Consolidated assets	181	'
Significant unconsolidated VIEs- Total assets	531	530
Significant unconsolidated VIEs- Maximum exposure to loss	200	206
Investment funds	'	'
Variable Interest Entity [Line Items]	'	'
Consolidated VIEs- Consolidated assets	1,508	1,175
Significant unconsolidated VIEs- Total assets	2,935	2,770
Significant unconsolidated VIEs- Maximum exposure to loss	387	302
Trust arrangements and other	'	'
Variable Interest Entity [Line Items]	'	'
Consolidated VIEs- Consolidated assets	¥ 38	¥ 39

Carrying_Amounts_and_Classific

Carrying Amounts and Classification of Assets and Liabilities on MHFG Group's Balance Sheets that Relate to its Variable Interests in Significant Unconsolidated VIEs (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Assets on balance sheets related to unconsolidated VIEs:	'	'	'
Trading account assets	¥ 27,408,259,000,000	¥ 34,066,555,000,000	'
Loans	72,858,777,000,000	69,060,526,000,000	'
Total	175,699,346,000,000	178,746,994,000,000	166,361,600,000,000
Liabilities on balance sheets and maximum exposure to loss related to unconsolidated VIEs:	'	'	'
Payables under securities lending transactions	6,265,875,000,000	11,496,178,000,000	'
Total	169,077,975,000,000	172,889,899,000,000	'
Maximum exposure to loss	626,000,000,000	545,000,000,000	'
Unconsolidated VIEs	'	'	'
Assets on balance sheets related to unconsolidated VIEs:	'	'	'
Trading account assets	29,000,000,000	46,000,000,000	'
Investments	222,000,000,000	206,000,000,000	'
Loans	316,000,000,000	308,000,000,000	'
Total	567,000,000,000	560,000,000,000	'
Liabilities on balance sheets and maximum exposure to loss related to unconsolidated VIEs:	'	'	'
Payables under securities lending transactions	4,000,000,000	14,000,000,000	'
Total	4,000,000,000	14,000,000,000	'
Maximum exposure to loss	¥ 626,000,000,000	¥ 545,000,000,000	'

Recovered_Sheet8

Variable Interest Entities and Securitizations - Additional Information (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Assets associated with securitization transactions	'	'
Variable Interest Entity [Line Items]	'	'
Transferred assets continue to be carried on the consolidated balance sheets	¥ 181	¥ 174
Assets associated with loan participation transactions	'	'
Variable Interest Entity [Line Items]	'	'
Transferred assets continue to be carried on the consolidated balance sheets	¥ 79	¥ 62

Details_of_Fees_and_Commission

Details of Fees and Commissions Income (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Principal Transaction Revenue [Line Items]	'	'	'
Securities-related business	¥ 170,311	¥ 132,787	¥ 116,567
Deposits, debentures and lending business	114,073	113,989	97,509
Remittance business	108,534	104,574	105,015
Trust fees	48,914	45,621	45,990
Fees for other customer services	233,931	215,837	210,332
Total	¥ 675,763	¥ 612,808	¥ 575,413

Net_Trading_Gains_and_Losses_D

Net Trading Gains and Losses (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Trading account gains (losses)-net	¥ (59,687)		¥ 534,100		¥ 333,315
Foreign exchange gains (losses)-net	25,631	[1]	20,514	[1]	98,054	[1]
Net trading gains (losses)	-34,056		554,614		431,369
Interest rate contracts	'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Trading account gains (losses)-net	-79,562	[2]	219,385	[2]	261,568	[2]
Foreign exchange contracts	'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Trading account gains (losses)-net	-13,167		-91,300		-146,258
Equity-related contracts	'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Trading account gains (losses)-net	-41,607	[2]	-59,462	[2]	-7,150	[2]
Credit-related contracts	'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Trading account gains (losses)-net	899	[3]	-174	[3]	-2,184	[3]
Other contracts	'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Trading account gains (losses)-net	-6,856		-2,378		283
Trading securities	'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Trading account gains (losses)-net	¥ 80,606		¥ 468,029		¥ 227,056
[1]	Amounts include realized and unrealized gains and losses on both derivative instruments and nonderivative instruments, such as translation gains and losses related to foreign currency-denominated available-for-sale securities for which the fair value option is elected in accordance with ASC 825.
[2]	The net gain (loss) excluded from the assessment of the effectiveness of fair value hedges is included in the above table.
[3]	Amounts do not include the net loss of ¥3,391 million, ¥6,703 million and ¥8,660 million on the credit derivatives hedging the credit risk of loans during the fiscal years ended March 31, 2012, 2013 and 2014, respectively. The net loss is recorded in Other noninterest expenses.

Net_Trading_Gains_and_Losses_P

Net Trading Gains and Losses (Parenthetical) (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Gains (losses) recorded in income	¥ (148,643)		¥ 59,446		¥ 102,939
Credit-related contracts	'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Gains (losses) recorded in income	-7,761	[1]	-6,877	[1]	-5,575	[1]
Loans related to credit derivatives | Credit-related contracts	'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'
Gains (losses) recorded in income	¥ (8,660)		¥ (6,703)		¥ (3,391)
[1]	Amounts include the net loss of ¥3,391 million, ¥6,703 million and ¥8,660 million on the credit derivatives hedging the credit risk of loans during the fiscal years ended March 31, 2012, 2013 and 2014, respectively.

Assets_and_Liabilities_Measure

Assets and Liabilities Measured at Fair Value on Recurring Basis Including those for Which MHFG Group has Elected Fair Value Option (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
Assets:	'		'
Available-for-sale securities	¥ 30,648,761,000,000		¥ 39,413,951,000,000
Fair Value, Measurements, Recurring	'		'
Assets:	'		'
Other investments	71,000,000,000		76,000,000,000
Total assets measured at fair value	58,128,000,000,000	[1]	73,557,000,000,000	[1]
Liabilities:	'		'
Trading securities sold, not yet purchased	4,350,000,000,000		3,520,000,000,000
Long-term debt	658,000,000,000	[2]	552,000,000,000	[2]
Total liabilities measured at fair value	15,483,000,000,000		17,321,000,000,000
Fair Value, Measurements, Recurring | Interest rate contracts	'		'
Assets:	'		'
Assets, derivatives	8,064,000,000,000		10,350,000,000,000
Liabilities:	'		'
Liabilities, derivatives	7,895,000,000,000		10,018,000,000,000
Fair Value, Measurements, Recurring | Foreign exchange contracts	'		'
Assets:	'		'
Assets, derivatives	2,354,000,000,000		3,099,000,000,000
Liabilities:	'		'
Liabilities, derivatives	2,351,000,000,000		2,983,000,000,000
Fair Value, Measurements, Recurring | Equity-related contracts	'		'
Assets:	'		'
Assets, derivatives	197,000,000,000		182,000,000,000
Liabilities:	'		'
Liabilities, derivatives	178,000,000,000		177,000,000,000
Fair Value, Measurements, Recurring | Credit-related contracts	'		'
Assets:	'		'
Assets, derivatives	49,000,000,000		59,000,000,000
Liabilities:	'		'
Liabilities, derivatives	34,000,000,000		44,000,000,000
Fair Value, Measurements, Recurring | Other contracts	'		'
Assets:	'		'
Assets, derivatives	23,000,000,000		38,000,000,000
Liabilities:	'		'
Liabilities, derivatives	17,000,000,000		27,000,000,000
Fair Value, Measurements, Recurring | Japanese government bonds	'		'
Assets:	'		'
Assets, trading securities	3,410,000,000,000	[3]	4,700,000,000,000	[3]
Available-for-sale securities	22,056,000,000,000		30,783,000,000,000
Fair Value, Measurements, Recurring | Japanese local government bonds	'		'
Assets:	'		'
Assets, trading securities	74,000,000,000	[3]	125,000,000,000	[3]
Available-for-sale securities	245,000,000,000		244,000,000,000
Fair Value, Measurements, Recurring | U.S. Treasury bonds and federal agency securities	'		'
Assets:	'		'
Assets, trading securities	4,027,000,000,000	[3]	6,083,000,000,000	[3]
Available-for-sale securities	154,000,000,000		178,000,000,000
Fair Value, Measurements, Recurring | Other foreign government bonds	'		'
Assets:	'		'
Assets, trading securities	2,841,000,000,000	[3]	2,429,000,000,000	[3]
Available-for-sale securities	721,000,000,000		598,000,000,000
Fair Value, Measurements, Recurring | Agency mortgage-backed securities	'		'
Assets:	'		'
Assets, trading securities	1,754,000,000,000	[3]	2,651,000,000,000	[3]
Available-for-sale securities	961,000,000,000		1,006,000,000,000
Fair Value, Measurements, Recurring | Residential mortgage-backed securities	'		'
Assets:	'		'
Assets, trading securities	78,000,000,000	[3]	100,000,000,000	[3]
Available-for-sale securities	332,000,000,000		442,000,000,000
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities	'		'
Assets:	'		'
Assets, trading securities	93,000,000,000	[3]	94,000,000,000	[3]
Available-for-sale securities	161,000,000,000		250,000,000,000
Fair Value, Measurements, Recurring | Certificates of deposit and commercial paper	'		'
Assets:	'		'
Assets, trading securities	969,000,000,000	[3]	1,318,000,000,000	[3]
Fair Value, Measurements, Recurring | Corporate bonds and other debt securities	'		'
Assets:	'		'
Assets, trading securities	2,122,000,000,000	[3]	1,643,000,000,000	[3]
Fair Value, Measurements, Recurring | Equity securities	'		'
Assets:	'		'
Assets, trading securities	1,353,000,000,000	[3]	1,196,000,000,000	[3]
Fair Value, Measurements, Recurring | Japanese corporate bonds and other debt securities	'		'
Assets:	'		'
Available-for-sale securities	2,028,000,000,000		2,215,000,000,000
Fair Value, Measurements, Recurring | Foreign corporate bonds and other debt securities	'		'
Assets:	'		'
Available-for-sale securities	569,000,000,000		559,000,000,000
Fair Value, Measurements, Recurring | Equity securities (marketable)	'		'
Assets:	'		'
Available-for-sale securities	3,422,000,000,000		3,139,000,000,000
Fair Value, Measurements, Recurring | Level 1	'		'
Assets:	'		'
Other investments	2,000,000,000		1,000,000,000
Total assets measured at fair value	36,522,000,000,000	[1]	48,289,000,000,000	[1]
Liabilities:	'		'
Trading securities sold, not yet purchased	3,862,000,000,000		3,338,000,000,000
Total liabilities measured at fair value	3,968,000,000,000		3,401,000,000,000
Fair Value, Measurements, Recurring | Level 1 | Interest rate contracts	'		'
Assets:	'		'
Assets, derivatives	43,000,000,000		7,000,000,000
Liabilities:	'		'
Liabilities, derivatives	42,000,000,000		8,000,000,000
Fair Value, Measurements, Recurring | Level 1 | Foreign exchange contracts	'		'
Assets:	'		'
Assets, derivatives	6,000,000,000		5,000,000,000
Liabilities:	'		'
Liabilities, derivatives	5,000,000,000		4,000,000,000
Fair Value, Measurements, Recurring | Level 1 | Equity-related contracts	'		'
Assets:	'		'
Assets, derivatives	60,000,000,000		45,000,000,000
Liabilities:	'		'
Liabilities, derivatives	58,000,000,000		51,000,000,000
Fair Value, Measurements, Recurring | Level 1 | Other contracts	'		'
Assets:	'		'
Assets, derivatives	1,000,000,000		'
Liabilities:	'		'
Liabilities, derivatives	1,000,000,000		'
Fair Value, Measurements, Recurring | Level 1 | Japanese government bonds	'		'
Assets:	'		'
Assets, trading securities	3,360,000,000,000	[3]	4,651,000,000,000	[3]
Available-for-sale securities	20,912,000,000,000		29,198,000,000,000
Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury bonds and federal agency securities	'		'
Assets:	'		'
Assets, trading securities	3,541,000,000,000	[3]	5,777,000,000,000	[3]
Available-for-sale securities	154,000,000,000		178,000,000,000
Fair Value, Measurements, Recurring | Level 1 | Other foreign government bonds	'		'
Assets:	'		'
Assets, trading securities	2,567,000,000,000	[3]	2,235,000,000,000	[3]
Available-for-sale securities	280,000,000,000		334,000,000,000
Fair Value, Measurements, Recurring | Level 1 | Agency mortgage-backed securities	'		'
Assets:	'		'
Assets, trading securities	1,390,000,000,000	[3]	2,055,000,000,000	[3]
Available-for-sale securities	105,000,000,000		144,000,000,000
Fair Value, Measurements, Recurring | Level 1 | Corporate bonds and other debt securities	'		'
Assets:	'		'
Assets, trading securities	38,000,000,000	[3]	50,000,000,000	[3]
Fair Value, Measurements, Recurring | Level 1 | Equity securities	'		'
Assets:	'		'
Assets, trading securities	714,000,000,000	[3]	622,000,000,000	[3]
Fair Value, Measurements, Recurring | Level 1 | Foreign corporate bonds and other debt securities	'		'
Assets:	'		'
Available-for-sale securities	1,000,000,000		12,000,000,000
Fair Value, Measurements, Recurring | Level 1 | Equity securities (marketable)	'		'
Assets:	'		'
Available-for-sale securities	3,348,000,000,000		2,975,000,000,000
Fair Value, Measurements, Recurring | Level 2	'		'
Assets:	'		'
Total assets measured at fair value	20,124,000,000,000	[1]	23,431,000,000,000	[1]
Liabilities:	'		'
Trading securities sold, not yet purchased	488,000,000,000		182,000,000,000
Long-term debt	157,000,000,000	[2]	171,000,000,000	[2]
Total liabilities measured at fair value	10,981,000,000,000		13,471,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Interest rate contracts	'		'
Assets:	'		'
Assets, derivatives	7,997,000,000,000		10,319,000,000,000
Liabilities:	'		'
Liabilities, derivatives	7,846,000,000,000		9,997,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Foreign exchange contracts	'		'
Assets:	'		'
Assets, derivatives	2,331,000,000,000		3,066,000,000,000
Liabilities:	'		'
Liabilities, derivatives	2,340,000,000,000		2,968,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Equity-related contracts	'		'
Assets:	'		'
Assets, derivatives	124,000,000,000		114,000,000,000
Liabilities:	'		'
Liabilities, derivatives	108,000,000,000		110,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Credit-related contracts	'		'
Assets:	'		'
Assets, derivatives	28,000,000,000		30,000,000,000
Liabilities:	'		'
Liabilities, derivatives	30,000,000,000		35,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Other contracts	'		'
Assets:	'		'
Assets, derivatives	18,000,000,000		18,000,000,000
Liabilities:	'		'
Liabilities, derivatives	12,000,000,000		8,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Japanese government bonds	'		'
Assets:	'		'
Assets, trading securities	50,000,000,000	[3]	49,000,000,000	[3]
Available-for-sale securities	1,144,000,000,000		1,585,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Japanese local government bonds	'		'
Assets:	'		'
Assets, trading securities	74,000,000,000	[3]	125,000,000,000	[3]
Available-for-sale securities	245,000,000,000		244,000,000,000
Fair Value, Measurements, Recurring | Level 2 | U.S. Treasury bonds and federal agency securities	'		'
Assets:	'		'
Assets, trading securities	486,000,000,000	[3]	306,000,000,000	[3]
Fair Value, Measurements, Recurring | Level 2 | Other foreign government bonds	'		'
Assets:	'		'
Assets, trading securities	274,000,000,000	[3]	194,000,000,000	[3]
Available-for-sale securities	441,000,000,000		264,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Agency mortgage-backed securities	'		'
Assets:	'		'
Assets, trading securities	364,000,000,000	[3]	596,000,000,000	[3]
Available-for-sale securities	856,000,000,000		862,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Residential mortgage-backed securities	'		'
Assets:	'		'
Available-for-sale securities	112,000,000,000		150,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Commercial mortgage-backed securities	'		'
Assets:	'		'
Assets, trading securities	2,000,000,000	[3]	3,000,000,000	[3]
Fair Value, Measurements, Recurring | Level 2 | Certificates of deposit and commercial paper	'		'
Assets:	'		'
Assets, trading securities	969,000,000,000	[3]	1,318,000,000,000	[3]
Fair Value, Measurements, Recurring | Level 2 | Corporate bonds and other debt securities	'		'
Assets:	'		'
Assets, trading securities	1,671,000,000,000	[3]	1,176,000,000,000	[3]
Fair Value, Measurements, Recurring | Level 2 | Equity securities	'		'
Assets:	'		'
Assets, trading securities	579,000,000,000	[3]	503,000,000,000	[3]
Fair Value, Measurements, Recurring | Level 2 | Japanese corporate bonds and other debt securities	'		'
Assets:	'		'
Available-for-sale securities	1,858,000,000,000		2,000,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Foreign corporate bonds and other debt securities	'		'
Assets:	'		'
Available-for-sale securities	427,000,000,000		345,000,000,000
Fair Value, Measurements, Recurring | Level 2 | Equity securities (marketable)	'		'
Assets:	'		'
Available-for-sale securities	74,000,000,000		164,000,000,000
Fair Value, Measurements, Recurring | Level 3	'		'
Assets:	'		'
Other investments	69,000,000,000		75,000,000,000
Total assets measured at fair value	1,482,000,000,000	[1]	1,837,000,000,000	[1]
Liabilities:	'		'
Long-term debt	501,000,000,000	[2]	381,000,000,000	[2]
Total liabilities measured at fair value	534,000,000,000		449,000,000,000
Fair Value, Measurements, Recurring | Level 3 | Interest rate contracts	'		'
Assets:	'		'
Assets, derivatives	24,000,000,000		24,000,000,000
Liabilities:	'		'
Liabilities, derivatives	7,000,000,000		13,000,000,000
Fair Value, Measurements, Recurring | Level 3 | Foreign exchange contracts	'		'
Assets:	'		'
Assets, derivatives	17,000,000,000		28,000,000,000
Liabilities:	'		'
Liabilities, derivatives	6,000,000,000		11,000,000,000
Fair Value, Measurements, Recurring | Level 3 | Equity-related contracts	'		'
Assets:	'		'
Assets, derivatives	13,000,000,000		23,000,000,000
Liabilities:	'		'
Liabilities, derivatives	12,000,000,000		16,000,000,000
Fair Value, Measurements, Recurring | Level 3 | Credit-related contracts	'		'
Assets:	'		'
Assets, derivatives	21,000,000,000		29,000,000,000
Liabilities:	'		'
Liabilities, derivatives	4,000,000,000		9,000,000,000
Fair Value, Measurements, Recurring | Level 3 | Other contracts	'		'
Assets:	'		'
Assets, derivatives	4,000,000,000		20,000,000,000
Liabilities:	'		'
Liabilities, derivatives	4,000,000,000		19,000,000,000
Fair Value, Measurements, Recurring | Level 3 | Residential mortgage-backed securities	'		'
Assets:	'		'
Assets, trading securities	78,000,000,000	[3]	100,000,000,000	[3]
Available-for-sale securities	220,000,000,000		292,000,000,000
Fair Value, Measurements, Recurring | Level 3 | Commercial mortgage-backed securities	'		'
Assets:	'		'
Assets, trading securities	91,000,000,000	[3]	91,000,000,000	[3]
Available-for-sale securities	161,000,000,000		250,000,000,000
Fair Value, Measurements, Recurring | Level 3 | Corporate bonds and other debt securities	'		'
Assets:	'		'
Assets, trading securities	413,000,000,000	[3]	417,000,000,000	[3]
Fair Value, Measurements, Recurring | Level 3 | Equity securities	'		'
Assets:	'		'
Assets, trading securities	60,000,000,000	[3]	71,000,000,000	[3]
Fair Value, Measurements, Recurring | Level 3 | Japanese corporate bonds and other debt securities	'		'
Assets:	'		'
Available-for-sale securities	170,000,000,000		215,000,000,000
Fair Value, Measurements, Recurring | Level 3 | Foreign corporate bonds and other debt securities	'		'
Assets:	'		'
Available-for-sale securities	¥ 141,000,000,000		¥ 202,000,000,000
[1]	Amounts include the investments measured at the NAV per share at March 31, 2013 and 2014, of ¥715 billion and ¥649 billion, respectively, of which ¥667 billion and ¥612 billion, respectively, are classified in Level 2, and ¥48 billion and ¥37 billion, respectively, are classified in Level 3. The amounts of unfunded commitments related to these investments at March 31, 2013 and 2014 were ¥24 billion and ¥23 billion, respectively.
[2]	Amounts represent items for which the Group elected the fair value option.
[3]	Trading securities include foreign currency denominated securities for which the MHFG Group elected the fair value option.

Assets_and_Liabilities_Measure1

Assets and Liabilities Measured at Fair Value on Recurring Basis Including those for Which MHFG Group has Elected Fair Value Option (Parenthetical) (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Investments measured at NAV per share	¥ 649	¥ 715
Unfunded commitments	23	24
Level 2	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Investments measured at NAV per share	612	667
Level 3	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Investments measured at NAV per share	¥ 37	¥ 48

Reconciliation_for_All_Assets_

Reconciliation for All Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs Level 3 (Detail) (JPY ¥)	12 Months Ended
In Billions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Trading securities sold, not yet purchased	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Gains (losses) in OCI	'		'
Transfers out of level 3	'		-1
Purchases (in billions of yen)	'		-41
Sales	'		42
Long-term debt	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	381		460
Gains (losses) in Earnings	4	[1]	-26	[1]
Gains (losses) in OCI	'		'
Transfers into Level 3	1		4
Transfers out of level 3	-1		-175
Issuances	197		142
Settlements	-73		-76
Ending Balance	501		381
Change in unrealized gain (losses) still held	5	[2]	-24	[2]
Trading securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Transfers into Level 3	4		17
Transfers out of level 3	-12		-11
Trading securities | Residential mortgage-backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	100		159
Gains (losses) in Earnings	10	[3]	17	[3]
Purchases (in billions of yen)	'		2
Sales	-4		-7
Issuances	'		'
Settlements	-28		-71
Ending Balance	78		100
Change in unrealized gain (losses) still held	7	[2]	6	[2]
Trading securities | Commercial mortgage-backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	91		26
Gains (losses) in Earnings	5	[3]	1	[3]
Purchases (in billions of yen)	'		72
Sales	'		-1
Issuances	'		'
Settlements	-5		-7
Ending Balance	91		91
Change in unrealized gain (losses) still held	4	[2]	'
Trading securities | Corporate bonds and other debt securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	417		355
Gains (losses) in Earnings	55	[3]	72	[3]
Transfers into Level 3	4		14
Transfers out of level 3	-12		-8
Purchases (in billions of yen)	503		609
Sales	-442		-544
Issuances	'		'
Settlements	-112		-81
Ending Balance	413		417
Change in unrealized gain (losses) still held	35	[2]	42	[2]
Trading securities | Equity securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	71		82
Gains (losses) in Earnings	6	[3]	4	[3]
Transfers into Level 3	'		3
Transfers out of level 3	'		-3
Purchases (in billions of yen)	8		10
Sales	-24		-25
Issuances	'		'
Settlements	-1		'
Ending Balance	60		71
Change in unrealized gain (losses) still held	'		-1	[2]
Derivative assets	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Transfers out of level 3	'		-21
Derivative assets | Interest rate contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	11	[4]	-10	[4]
Gains (losses) in Earnings	6	[3],[4]	16	[3],[4]
Transfers into Level 3	-1	[4]	'
Issuances	'	[4]	'	[4]
Settlements	1	[4]	5	[4]
Ending Balance	17	[4]	11	[4]
Change in unrealized gain (losses) still held	11	[2],[4]	16	[2],[4]
Derivative assets | Foreign exchange contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	17	[4]	37	[4]
Gains (losses) in Earnings	-3	[3],[4]	-18	[3],[4]
Transfers out of level 3	'		-8	[4]
Issuances	'	[4]	'	[4]
Settlements	-3	[4]	6	[4]
Ending Balance	11	[4]	17	[4]
Change in unrealized gain (losses) still held	5	[2],[4]	-21	[2],[4]
Derivative assets | Equity-related contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	7	[4]	22	[4]
Gains (losses) in Earnings	-6	[3],[4]	-10	[3],[4]
Issuances	'	[4]	'	[4]
Settlements	'		-5	[4]
Ending Balance	1	[4]	7	[4]
Change in unrealized gain (losses) still held	-7	[2],[4]	-10	[2],[4]
Derivative assets | Credit-related contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	20	[4]	23	[4]
Gains (losses) in Earnings	-6	[3],[4]	-6	[3],[4]
Transfers into Level 3	'		-1	[4]
Transfers out of level 3	1	[4]	1	[4]
Issuances	'	[4]	'	[4]
Settlements	2	[4]	3	[4]
Ending Balance	17	[4]	20	[4]
Change in unrealized gain (losses) still held	-6	[2],[4]	-5	[2],[4]
Derivative assets | Other contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	1	[4]	15	[4]
Transfers out of level 3	'		-14	[4]
Issuances	'	[4]	'	[4]
Settlements	-1	[4]	'
Ending Balance	'		1	[4]
Available-for-sale securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Transfers into Level 3	7		'
Transfers out of level 3	-30		'
Available-for-sale securities | Residential mortgage-backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	292		348
Gains (losses) in Earnings	-1	[5]	'
Gains (losses) in OCI	5	[6]	6	[6]
Purchases (in billions of yen)	5		29
Sales	-9		-1
Issuances	'		'
Settlements	-72		-90
Ending Balance	220		292
Available-for-sale securities | Commercial mortgage-backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	250		330
Gains (losses) in Earnings	5	[5]	2	[5]
Gains (losses) in OCI	-2	[6]	12	[6]
Purchases (in billions of yen)	36		31
Sales	-18		-16
Issuances	'		'
Settlements	-110		-109
Ending Balance	161		250
Change in unrealized gain (losses) still held	-1	[2]	-5	[2]
Available-for-sale securities | Japanese corporate bonds and other debt securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	215		226
Gains (losses) in OCI	'		1	[6]
Transfers out of level 3	-30		'
Purchases (in billions of yen)	60		95
Sales	-1		'
Issuances	'		'
Settlements	-74		-107
Ending Balance	170		215
Available-for-sale securities | Foreign corporate bonds and other debt securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	202		236
Gains (losses) in Earnings	8	[5]	4	[5]
Gains (losses) in OCI	-1	[6]	6	[6]
Transfers into Level 3	7		'
Purchases (in billions of yen)	'		28
Sales	'		-4
Issuances	'		'
Settlements	-75		-68
Ending Balance	141		202
Other investments	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Beginning Balance	75		189
Gains (losses) in Earnings	-2	[5]	12	[5]
Transfers out of level 3	-2		'
Purchases (in billions of yen)	7		6
Sales	-2		-49
Issuances	'		'
Settlements	-7		-83
Ending Balance	69		75
Change in unrealized gain (losses) still held	¥ (2)	[2]	'
[1]	Gains (losses) in Earnings are reported in Other noninterest income (expenses).
[2]	Amounts represent total gains or losses recognized in earnings during the period. These gains or losses are attributable to the change in fair value relating to assets and liabilities classified as Level 3 that are still held at March 31, 2013 and 2014.
[3]	Gains (losses) in Earnings are reported in Trading account gains (losses)-net, Foreign exchange gains (losses)-net or Other noninterest income (expenses).
[4]	Total Level 3 derivative exposures have been netted on the table for presentation purposes only.
[5]	Gains (losses) in Earnings are reported in Investment gains (losses)-net.
[6]	Gains (losses) in OCI are reported in Accumulated other comprehensive income (loss).

Fair_Value_Additional_Informat

Fair Value - Additional Information (Detail) (JPY ¥)	12 Months Ended
In Billions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]	'	'
Carrying amounts of other equity interests of which fair value is not readily determinable	¥ 526	¥ 537
Derivative liabilities	'	'
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]	'	'
Fair value of liabilities transferred into Level 3	1	1
Fair value of liabilities transferred out of Level 3	1	'
Long-term debt	'	'
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]	'	'
Fair value of liabilities transferred into Level 3	1	4
Fair value of liabilities transferred out of Level 3	1	175
Trading securities sold, not yet purchased	'	'
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]	'	'
Fair value of liabilities transferred out of Level 3	'	1
Trading securities	'	'
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]	'	'
Fair value of assets transferred from Level 1 to Level 2	'	37
Fair value of assets transferred into Level 3	4	17
Fair value of assets transferred out of Level 3	12	11
Derivative assets	'	'
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]	'	'
Fair value of assets transferred out of Level 3	'	21
Available-for-sale securities	'	'
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]	'	'
Fair value of assets transferred into Level 3	7	'
Fair value of assets transferred out of Level 3	30	'
Other investments	'	'
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]	'	'
Fair value of assets transferred out of Level 3	2	'
Structured notes	'	'
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]	'	'
The differences between the aggregate fair value and aggregate unpaid principal balance of the notes for which the fair value option has been elected	14	9
Net unrealized gains (losses) resulting from changes in fair values of the notes	¥ 4	¥ (30)

Quantitative_Information_About

Quantitative Information About Level Three Fair Value Measurements (Detail) (JPY ¥)	12 Months Ended
In Billions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Available For Sale And Trading Securities | Residential mortgage-backed securities	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Fair value	¥ 298		¥ 392
Principal valuation technique	'Discounted cash flow Price-based		'Discounted cash flow Price-based
Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flow Method Or Transaction Price Valuation Technique | Minimum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Prepayment rate	1.00%		0.00%
Default rate	0.00%		0.00%
Recovery rate	70.00%		70.00%
Discount margin	0.08%		0.07%
Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flow Method Or Transaction Price Valuation Technique | Maximum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Prepayment rate	24.00%		24.00%
Default rate	4.00%		5.00%
Recovery rate	100.00%		100.00%
Discount margin	20.02%		26.16%
Available For Sale And Trading Securities | Commercial mortgage-backed securities	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Fair value	252		341
Principal valuation technique	'Discounted cash flow Price-based		'Discounted cash flow Price-based
Available For Sale And Trading Securities | Commercial mortgage-backed securities | Discounted Cash Flow Method Or Transaction Price Valuation Technique | Minimum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Discount margin	0.17%		0.09%
Available For Sale And Trading Securities | Commercial mortgage-backed securities | Discounted Cash Flow Method Or Transaction Price Valuation Technique | Maximum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Discount margin	34.41%		39.29%
Available For Sale And Trading Securities | Corporate bonds and other debt securities	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Fair value	724		834
Principal valuation technique	'Discounted cash flow Price-based		'Discounted cash flow Price-based
Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flow Method Or Transaction Price Valuation Technique | Minimum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Prepayment rate	0.00%	[1]	0.00%	[1]
Default rate	0.00%	[1]	0.00%	[1]
Recovery rate	15.00%	[1]	15.00%	[1]
Discount margin	0.12%	[1]	0.00%	[1]
Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flow Method Or Transaction Price Valuation Technique | Maximum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Prepayment rate	42.00%	[1]	43.00%	[1]
Default rate	9.00%	[1]	8.00%	[1]
Recovery rate	75.00%	[1]	85.00%	[1]
Discount margin	17.25%	[1]	49.18%	[1]
Available For Sale And Trading Securities | Japanese corporate bonds and foreign corporate bonds | Discounted Cash Flow Method Or Transaction Price Valuation Technique | Minimum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Discount margin	-1.22%	[2]	0.00%	[2]
Available For Sale And Trading Securities | Japanese corporate bonds and foreign corporate bonds | Discounted Cash Flow Method Or Transaction Price Valuation Technique | Maximum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Discount margin	13.03%	[2]	12.32%	[2]
Derivative contracts | Interest rate contracts	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Fair value	17		11
Principal valuation technique	'Internal valuation model	[3]	'Internal valuation model	[3]
Derivative contracts | Interest rate contracts | Internal Valuation Model | Minimum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
IR - IR correlation	23.00%		42.00%
Default rate	0.00%	[4]	0.00%	[4]
Derivative contracts | Interest rate contracts | Internal Valuation Model | Maximum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
IR - IR correlation	100.00%		100.00%
Default rate	63.00%	[4]	63.00%	[4]
Derivative contracts | Foreign exchange contracts	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Fair value	11		17
Principal valuation technique	'Internal valuation model	[3]	'Internal valuation model	[3]
Derivative contracts | Foreign exchange contracts | Internal Valuation Model | Minimum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
FX - IR correlation	28.00%		36.00%
FX - FX correlation	55.00%		55.00%
FX volatility	14.00%		16.00%
Default rate	0.00%	[4]	0.00%	[4]
Derivative contracts | Foreign exchange contracts | Internal Valuation Model | Maximum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
FX - IR correlation	52.00%		55.00%
FX - FX correlation	55.00%		55.00%
FX volatility	25.00%		26.00%
Default rate	63.00%	[4]	63.00%	[4]
Derivative contracts | Equity-related contracts	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Fair value	1		7
Principal valuation technique	'Internal valuation model	[3]	'Internal valuation model	[3]
Derivative contracts | Equity-related contracts | Internal Valuation Model | Minimum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Equity - IR correlation	0.00%		0.00%
Equity - FX correlation	0.00%		0.00%
Equity volatility	18.00%		14.00%
Derivative contracts | Equity-related contracts | Internal Valuation Model | Maximum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Equity - IR correlation	60.00%		60.00%
Equity - FX correlation	70.00%		70.00%
Equity volatility	35.00%		48.00%
Derivative contracts | Credit-related contracts	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Fair value	17	[5]	20	[5]
Principal valuation technique	'Internal valuation model	[3],[5]	'Internal valuation model	[3],[5]
Derivative contracts | Credit-related contracts | Internal Valuation Model | Minimum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Default rate	0.00%		0.00%
Credit correlation	1.00%		2.00%
Derivative contracts | Credit-related contracts | Internal Valuation Model | Maximum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Default rate	47.00%		67.00%
Credit correlation	100.00%		100.00%
Long-term debt	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
Fair value	¥ 501		¥ 381
Principal valuation technique	'Internal valuation model	[3]	'Internal valuation model	[3]
Long-term debt | Internal Valuation Model | Minimum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
IR - IR correlation	23.00%		42.00%
FX - IR correlation	28.00%		36.00%
FX - FX correlation	55.00%		55.00%
Default rate	0.00%		0.00%
Equity - IR correlation	0.00%		0.00%
Credit correlation	19.00%		2.00%
Equity - FX correlation	0.00%		'
Equity volatility	13.00%		18.00%
Long-term debt | Internal Valuation Model | Maximum	'		'
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'		'
IR - IR correlation	100.00%		100.00%
FX - IR correlation	52.00%		55.00%
FX - FX correlation	55.00%		55.00%
Default rate	5.00%		10.00%
Equity - IR correlation	60.00%		60.00%
Credit correlation	100.00%		100.00%
Equity - FX correlation	70.00%		'
Equity volatility	37.00%		48.00%
[1]	These inputs are mainly used for determining the fair values of securitization products such as CDO, CLO and ABS, other than RMBS and CMBS.
[2]	This input is mainly used for determining the fair values of Japanese corporate bonds and foreign corporate bonds.
[3]	Internal valuation model includes discounted cash flow models and the Black-Scholes option pricing model.
[4]	This input represents the counterparty default rate derived from the MHFG Group's own internal credit analysis.
[5]	The majority of the fair value of credit derivatives in Level 3 relates to credit derivatives economically hedging the credit risk in certain securitization products. The unobservable inputs of these credit derivatives have already been included in the unobservable inputs related to Trading securities and Available-for-sale securities disclosed above.

Fair_Value_Hierarchy_for_Asset

Fair Value Hierarchy for Assets and Liabilities Measured on Nonrecurring Basis (Detail) (Fair Value, Measurements, Nonrecurring, JPY ¥)	Mar. 31, 2014	Mar. 31, 2013
In Billions, unless otherwise specified
Assets:	'	'
Loans	¥ 124	¥ 222
Loans held-for-sale	33	5
Other investments	5	11
Premises and equipment-net	1	1
Total assets at fair value	163	239
Level 2	'	'
Assets:	'	'
Loans held-for-sale	'	5
Total assets at fair value	'	5
Level 3	'	'
Assets:	'	'
Loans	124	222
Loans held-for-sale	33	'
Other investments	5	11
Premises and equipment-net	1	1
Total assets at fair value	163	234
Aggregate cost	'	'
Assets:	'	'
Loans	208	343
Loans held-for-sale	34	5
Other investments	6	16
Premises and equipment-net	2	5
Goodwill	4	'
Total assets at fair value	¥ 254	¥ 369

Carrying_Amounts_and_Fair_Valu

Carrying Amounts and Fair Values of Certain Financial Instruments Excluding Financial Instruments Which Are Carried at Fair Value on a Recurring Basis and Those Outside Scope of Asc 825 (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Billions, unless otherwise specified
Carrying amount	'		'
Financial assets:	'		'
Cash and due from banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions	¥ 34,563		¥ 27,583
Investments	4,040		3,000
Loans, net of allowance for loan losses	72,801	[1]	69,028	[1]
Financial liabilities:	'		'
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions	44,124		48,048
Interest-bearing deposits	88,744		87,247
Due to trust accounts	742		619
Other short-term borrowings	6,024		6,724
Long-term debt	9,176		8,235
Estimated fair value	'		'
Financial assets:	'		'
Cash and due from banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions	34,563		27,583
Investments	4,058		3,020
Loans, net of allowance for loan losses	73,975	[1]	70,261	[1]
Financial liabilities:	'		'
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions	44,124		48,048
Interest-bearing deposits	88,705		87,210
Due to trust accounts	742		619
Other short-term borrowings	6,024		6,723
Long-term debt	9,441		8,598
Estimated fair value | Level 1	'		'
Financial assets:	'		'
Cash and due from banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions	1,437		903
Investments	4,058		3,020
Financial liabilities:	'		'
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions	13,543		12,796
Interest-bearing deposits	37,394		34,596
Estimated fair value | Level 2	'		'
Financial assets:	'		'
Cash and due from banks, call loans and funds sold, and receivables under resale agreements and securities borrowing transactions	33,126		26,680
Financial liabilities:	'		'
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions	30,581		35,252
Interest-bearing deposits	51,311		52,614
Due to trust accounts	742		619
Other short-term borrowings	6,024		6,723
Long-term debt	8,600		7,967
Estimated fair value | Level 3	'		'
Financial assets:	'		'
Loans, net of allowance for loan losses	73,975	[1]	70,261	[1]
Financial liabilities:	'		'
Long-term debt	¥ 841		¥ 631
[1]	Loans, net of allowance for loan losses include items measured at fair value on a nonrecurring basis.

Information_of_Offsetting_of_F

Information of Offsetting of Financial Assets and Financial Liabilities (Detail) (JPY ¥)	Mar. 31, 2014		Mar. 31, 2013
In Billions, unless otherwise specified
Offsetting Financial Assets And Financial Liabilities [Line Items]	'		'
Derivative assets, Gross amounts recognized	¥ 9,880	[1]	¥ 13,019	[1]
Derivative assets, Gross amounts offset on the balance sheet	'	[1]	'	[1]
Derivative assets, Net amounts presented on the balance sheet	9,880	[1],[2]	13,019	[1],[2]
Derivative assets, Amounts not offset on the balance sheet, Financial instruments	8,702	[1],[3],[4]	11,289	[1],[3],[4]
Derivative assets, Amounts not offset on the balance sheet, Cash collateral	406	[1],[3]	446	[1],[3]
Derivative assets, Net amounts	772	[1]	1,284	[1]
Receivables under resale agreements, Gross amounts recognized	8,236	[1]	8,869	[1]
Receivables under resale agreements, Gross amounts offset on the balance sheet	'	[1]	'	[1]
Receivables under resale agreements, Net amounts presented on the balance sheet	8,236	[1],[2]	8,869	[1],[2]
Receivables under resale agreements, Amounts not offset on the balance sheet, Financial instruments	8,200	[1],[3],[4]	8,812	[1],[3],[4]
Receivables under resale agreements, Amounts not offset on the balance sheet, Cash collateral	'	[1],[3]	'	[1],[3]
Receivables under resale agreements, Net amounts	36	[1]	57	[1]
Receivables under securities borrowing transactions, Gross amounts recognized	4,990	[1]	5,544	[1]
Receivables under securities borrowing transactions, Gross amounts offset on the balance sheet	'	[1]	'	[1]
Receivables under securities borrowing transactions, Net amounts presented on the balance sheet	4,990	[1],[2]	5,544	[1],[2]
Receivables under securities borrowing transactions, Amounts not offset on the balance sheet, Financial instruments	4,978	[1],[3],[4]	5,534	[1],[3],[4]
Receivables under securities borrowing transactions, Amounts not offset on the balance sheet, Cash collateral	'	[1],[3]	'	[1],[3]
Receivables under securities borrowing transactions, Net amounts	12	[1]	10	[1]
Financial assets, Gross amounts recognized, Total	23,106	[1]	27,432	[1]
Financial assets, Gross amounts offset on the balance sheet, Total	'	[1]	'	[1]
Financial assets, Net amounts presented on the balance sheet, Total	23,106	[1],[2]	27,432	[1],[2]
Financial assets, Amounts not offset on the balance sheet, Financial instruments, Total	21,880	[1],[3],[4]	25,635	[1],[3],[4]
Financial assets, Amounts not offset on the balance sheet, Cash collateral, Total	406	[1],[3]	446	[1],[3]
Financial assets, Net amounts, Total	820	[1]	1,351	[1]
Derivative liabilities, Gross amounts recognized	9,648	[1]	12,712	[1]
Derivative liabilities, Gross amounts offset on the balance sheet	'	[1]	'	[1]
Derivative liabilities, Net amounts presented on the balance sheet	9,648	[1],[2]	12,712	[1],[2]
Derivative liabilities, Amounts not offset on the balance sheet, Financial instruments	8,621	[1],[3],[4]	11,234	[1],[3],[4]
Derivative liabilities, Amounts not offset on the balance sheet, Cash collateral	431	[1],[3]	653	[1],[3]
Derivative liabilities, Net amounts	596	[1]	825	[1]
Payables under repurchase agreements, Gross amounts recognized	16,690	[1]	17,397	[1]
Payables under repurchase agreements, Gross amounts offset on the balance sheet	'	[1]	'	[1]
Payables under repurchase agreements, Net amounts presented on the balance sheet	16,690	[1],[2]	17,397	[1],[2]
Payables under repurchase agreements, Amounts not offset on the balance sheet, Financial instruments	16,667	[1],[3],[4]	17,280	[1],[3],[4]
Payables under repurchase agreements, Amounts not offset on the balance sheet, Cash collateral	'	[1],[3]	'	[1],[3]
Payables under repurchase agreements, Net amounts	23	[1]	117	[1]
Payables under securities lending transactions, Gross amounts recognized	6,085	[1]	11,326	[1]
Payables under securities lending transactions, Gross amounts offset on the balance sheet	'	[1]	'	[1]
Payables under securities lending transactions, Net amounts presented on the balance sheet	6,085	[1],[2]	11,326	[1],[2]
Payables under securities lending transactions, Amounts not offset on the balance sheet, Financial instruments	6,082	[1],[3],[4]	11,320	[1],[3],[4]
Payables under securities lending transactions, Amounts not offset on the balance sheet, Cash collateral	'	[1],[3]	'	[1],[3]
Payables under securities lending transactions, Net amounts	3	[1]	6	[1]
Financial liabilities, Gross amounts recognized, Total	32,423	[1]	41,435	[1]
Financial liabilities, Gross amounts offset on the balance sheet, Total	'	[1]	'	[1]
Financial liabilities, Net amounts presented on the balance sheet, Total	32,423	[1],[2]	41,435	[1],[2]
Financial liabilities, Amounts not offset on the balance sheet, Financial instruments, Total	31,370	[1],[3],[4]	39,834	[1],[3],[4]
Financial liabilities, Amounts not offset on the balance sheet, Cash collateral, Total	431	[1],[3]	653	[1],[3]
Financial liabilities, Net amounts, Total	¥ 622	[1]	¥ 948	[1]
[1]	Amounts relating to master netting arrangements or similar agreements where the Group does not have the legal right of set-off or where uncertainty exists as to the enforceability of these agreements are excluded. For derivatives, the table includes amounts relating to over-the-counter ("OTC") and OTC-cleared derivatives that are subject to enforceable master netting arrangements or similar agreements.
[2]	Derivative assets and liabilities are recorded in Trading account assets and Trading account liabilities, respectively.
[3]	Amounts do not exceed the net amounts presented on the balance sheet and do not include the effect of overcollateralization, where it exists.
[4]	For derivatives, amounts include derivative assets or liabilities and securities collateral that are eligible for offsetting under enforceable master netting arrangements or similar agreements.

Information_for_Reportable_Seg

Information for Reportable Segments (Detail) (JPY ¥)	12 Months Ended
In Billions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Gross profits:	'		'		'
Net interest income (expense)	¥ 1,108.3	[1],[2],[3],[4]	¥ 1,075.9	[1],[2],[3]	¥ 1,088.3	[1]
Net noninterest income (expenses)	927	[1],[2],[3],[4]	1,095.80	[1],[2],[3]	914.8	[1]
Total	2,035.30	[1],[2],[3],[4]	2,171.70	[1],[2],[3]	2,003.10	[1]
General and administrative expenses	1,229.30	[1],[2],[3],[4]	1,171	[1],[2],[3]	1,206.30	[1]
Others	-61.7	[1],[2],[3],[4]	-88.5	[1],[2],[3]	-77.7	[1]
Net business profits	744.3	[1],[2],[3],[4]	912.2	[1],[2],[3]	719.1	[1]
Others	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	131.4	[1],[2],[3],[4]	-0.3	[1],[2],[3]	-6.4	[1]
Net noninterest income (expenses)	127.6	[1],[2],[3],[4]	57.7	[1],[2],[3]	54.8	[1]
Total	259	[1],[2],[3],[4]	57.4	[1],[2],[3]	48.4	[1]
General and administrative expenses	180.9	[1],[2],[3],[4]	40.8	[1],[2],[3]	40.1	[1]
Others	-2.7	[1],[2],[3],[4]	-27.6	[1],[2],[3]	-7.9	[1]
Net business profits	75.4	[1],[2],[3],[4]	-11	[1],[2],[3]	0.4	[1]
MizuhoTrust Banking Company Limited Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	40.2	[1],[2],[3],[4]	39.5	[1],[2],[3]	42.5	[1]
Net noninterest income (expenses)	108.1	[1],[2],[3],[4]	105	[1],[2],[3]	104.8	[1]
Total	148.3	[1],[2],[3],[4]	144.5	[1],[2],[3]	147.3	[1]
General and administrative expenses	90.9	[1],[2],[3],[4]	90.1	[1],[2],[3]	92.3	[1]
Others	-2.9	[1],[2],[3],[4]	-3.5	[1],[2],[3]	-3.7	[1]
Net business profits	54.5	[1],[2],[3],[4]	50.9	[1],[2],[3]	51.3	[1]
Mizuho Securities Company Limited Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	2.9	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	283.9	[1],[2],[3],[4]	'		'
Total	286.8	[1],[2],[3],[4]	'		'
General and administrative expenses	246.2	[1],[2],[3],[4]	'		'
Net business profits	40.6	[1],[2],[3],[4]	'		'
Mizuho Bank Limited And Mizuho Corporate Bank Limited	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	923.8		915.5		940.4
Net noninterest income (expenses)	460.3		647.1		540.1
Total	1,384.10		1,562.60		1,480.50
General and administrative expenses	791.1		765.5		801.3
Net business profits	593		797.1		679.2
Mizuho Bank Limited And Mizuho Corporate Bank Limited | Personal Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	218.5		219.2		224.3
Net noninterest income (expenses)	41.6		33.9		32.1
Total	260.1		253.1		256.4
General and administrative expenses	226.4		218.6		218.6
Net business profits	33.7		34.5		37.8
Mizuho Bank Limited And Mizuho Corporate Bank Limited | Retail banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	80		83.3		95.1
Net noninterest income (expenses)	45.3		42.3		41
Total	125.3		125.6		136.1
General and administrative expenses	116.7		113.7		108.2
Net business profits	8.6		11.9		27.9
Mizuho Bank Limited And Mizuho Corporate Bank Limited | Corporate Banking (Large Corporations)	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	172.7		155.8		168.4
Net noninterest income (expenses)	131.4		122.6		133.4
Total	304.1		278.4		301.8
General and administrative expenses	87.2		88.4		94.1
Net business profits	216.9		190		207.7
Mizuho Bank Limited And Mizuho Corporate Bank Limited | Corporate Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	103.3		106.6		121.3
Net noninterest income (expenses)	64.7		70.9		69.3
Total	168		177.5		190.6
General and administrative expenses	77.7		74.5		87.7
Net business profits	90.3		103		102.9
Mizuho Bank Limited And Mizuho Corporate Bank Limited | Financial Institution & Public Sector Business	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	35.4		36.2		40.3
Net noninterest income (expenses)	22.3		24.2		24.4
Total	57.7		60.4		64.7
General and administrative expenses	29		26.5		26.1
Net business profits	28.7		33.9		38.6
Mizuho Bank Limited And Mizuho Corporate Bank Limited | Trading and others	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	185		206.2		200.7
Net noninterest income (expenses)	15.2		248.5		153
Total	200.2		454.7		353.7
General and administrative expenses	171.6		177.2		206.3
Net business profits	28.6		277.5		147.4
Mizuho Bank Limited And Mizuho Corporate Bank Limited | International Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	128.9		108.2		90.3
Net noninterest income (expenses)	139.8		104.7		86.9
Total	268.7		212.9		177.2
General and administrative expenses	82.5		66.6		60.3
Net business profits	186.2		146.3		116.9
Former Mizuho Bank, Limited Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		550.6	[1],[2],[3]	583.9	[1]
Net noninterest income (expenses)	'		360.3	[1],[2],[3]	305.8	[1]
Total	'		910.9	[1],[2],[3]	889.7	[1]
General and administrative expenses	'		568.2	[1],[2],[3]	608.5	[1]
Others	'		-7.4	[1],[2],[3]	-14	[1]
Net business profits	'		335.3	[1],[2],[3]	267.2	[1]
Former Mizuho Bank, Limited Consolidated | Former Mizuho Bank, Limited Non-Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		513.8	[1],[2],[3]	545.4	[1]
Net noninterest income (expenses)	'		313.7	[1],[2],[3]	253.3	[1]
Total	'		827.5	[1],[2],[3]	798.7	[1]
General and administrative expenses	'		524.4	[1],[2],[3]	556.4	[1]
Net business profits	'		303.1	[1],[2],[3]	242.3	[1]
Former Mizuho Bank, Limited Consolidated | Former Mizuho Bank, Limited Non-Consolidated | Personal Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		219.2	[1],[2],[3]	224.3	[1]
Net noninterest income (expenses)	'		33.9	[1],[2],[3]	32.1	[1]
Total	'		253.1	[1],[2],[3]	256.4	[1]
General and administrative expenses	'		218.6	[1],[2],[3]	218.6	[1]
Net business profits	'		34.5	[1],[2],[3]	37.8	[1]
Former Mizuho Bank, Limited Consolidated | Former Mizuho Bank, Limited Non-Consolidated | Retail banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		83.3	[1],[2],[3]	95.1	[1]
Net noninterest income (expenses)	'		42.3	[1],[2],[3]	41	[1]
Total	'		125.6	[1],[2],[3]	136.1	[1]
General and administrative expenses	'		113.7	[1],[2],[3]	108.2	[1]
Net business profits	'		11.9	[1],[2],[3]	27.9	[1]
Former Mizuho Bank, Limited Consolidated | Former Mizuho Bank, Limited Non-Consolidated | Corporate Banking (Large Corporations)	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		14.9	[1],[2],[3]	17.8	[1]
Net noninterest income (expenses)	'		19.3	[1],[2],[3]	19	[1]
Total	'		34.2	[1],[2],[3]	36.8	[1]
General and administrative expenses	'		11.6	[1],[2],[3]	18.5	[1]
Net business profits	'		22.6	[1],[2],[3]	18.3	[1]
Former Mizuho Bank, Limited Consolidated | Former Mizuho Bank, Limited Non-Consolidated | Corporate Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		106.1	[1],[2],[3]	118.6	[1]
Net noninterest income (expenses)	'		70.7	[1],[2],[3]	68.2	[1]
Total	'		176.8	[1],[2],[3]	186.8	[1]
General and administrative expenses	'		73.2	[1],[2],[3]	86.4	[1]
Net business profits	'		103.6	[1],[2],[3]	100.4	[1]
Former Mizuho Bank, Limited Consolidated | Former Mizuho Bank, Limited Non-Consolidated | Financial Institution & Public Sector Business	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		19.9	[1],[2],[3]	22.2	[1]
Net noninterest income (expenses)	'		11	[1],[2],[3]	8.6	[1]
Total	'		30.9	[1],[2],[3]	30.8	[1]
General and administrative expenses	'		14.3	[1],[2],[3]	14.5	[1]
Net business profits	'		16.6	[1],[2],[3]	16.3	[1]
Former Mizuho Bank, Limited Consolidated | Former Mizuho Bank, Limited Non-Consolidated | Trading and others	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		70.4	[1],[2],[3]	67.4	[1]
Net noninterest income (expenses)	'		136.5	[1],[2],[3]	84.4	[1]
Total	'		206.9	[1],[2],[3]	151.8	[1]
General and administrative expenses	'		93	[1],[2],[3]	110.2	[1]
Net business profits	'		113.9	[1],[2],[3]	41.6	[1]
Former Mizuho Bank, Limited Consolidated | Former Mizuho Investors Securities Company Limited, Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		'		0.7	[1]
Net noninterest income (expenses)	'		'		43.9	[1]
Total	'		'		44.6	[1]
General and administrative expenses	'		'		40.9	[1]
Net business profits	'		'		3.7	[1]
Former Mizuho Bank, Limited Consolidated | Others	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		36.8	[1],[2],[3]	37.8	[1]
Net noninterest income (expenses)	'		46.6	[1],[2],[3]	8.6	[1]
Total	'		83.4	[1],[2],[3]	46.4	[1]
General and administrative expenses	'		43.8	[1],[2],[3]	11.2	[1]
Others	'		-7.4	[1],[2],[3]	-14	[1]
Net business profits	'		32.2	[1],[2],[3]	21.2	[1]
Former Mizuho Corporate Bank, Limited Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		486.1	[1],[2],[3]	468.3	[1]
Net noninterest income (expenses)	'		572.8	[1],[2],[3]	449.4	[1]
Total	'		1,058.90	[1],[2],[3]	917.7	[1]
General and administrative expenses	'		471.9	[1],[2],[3]	465.4	[1]
Others	'		-50	[1],[2],[3]	-52.1	[1]
Net business profits	'		537	[1],[2],[3]	400.2	[1]
Former Mizuho Corporate Bank, Limited Consolidated | Others	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		86.2	[1],[2],[3]	81.4	[1]
Net noninterest income (expenses)	'		10.4	[1],[2],[3]	10.9	[1]
Total	'		96.6	[1],[2],[3]	92.3	[1]
General and administrative expenses	'		33.7	[1],[2],[3]	27.6	[1]
Others	'		-50	[1],[2],[3]	-52	[1]
Net business profits	'		12.9	[1],[2],[3]	12.7	[1]
Former Mizuho Corporate Bank, Limited Consolidated | Former Mizuho Corporate Bank, Limited Non-consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		401.7	[1],[2],[3]	395	[1]
Net noninterest income (expenses)	'		333.4	[1],[2],[3]	286.8	[1]
Total	'		735.1	[1],[2],[3]	681.8	[1]
General and administrative expenses	'		241.1	[1],[2],[3]	244.9	[1]
Net business profits	'		494	[1],[2],[3]	436.9	[1]
Former Mizuho Corporate Bank, Limited Consolidated | Former Mizuho Corporate Bank, Limited Non-consolidated | Corporate Banking (Large Corporations)	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		140.9	[1],[2],[3]	150.6	[1]
Net noninterest income (expenses)	'		103.3	[1],[2],[3]	114.4	[1]
Total	'		244.2	[1],[2],[3]	265	[1]
General and administrative expenses	'		76.8	[1],[2],[3]	75.6	[1]
Net business profits	'		167.4	[1],[2],[3]	189.4	[1]
Former Mizuho Corporate Bank, Limited Consolidated | Former Mizuho Corporate Bank, Limited Non-consolidated | Corporate Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		0.5	[1],[2],[3]	2.7	[1]
Net noninterest income (expenses)	'		0.2	[1],[2],[3]	1.1	[1]
Total	'		0.7	[1],[2],[3]	3.8	[1]
General and administrative expenses	'		1.3	[1],[2],[3]	1.3	[1]
Net business profits	'		-0.6	[1],[2],[3]	2.5	[1]
Former Mizuho Corporate Bank, Limited Consolidated | Former Mizuho Corporate Bank, Limited Non-consolidated | Financial Institution & Public Sector Business	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		16.3	[1],[2],[3]	18.1	[1]
Net noninterest income (expenses)	'		13.2	[1],[2],[3]	15.8	[1]
Total	'		29.5	[1],[2],[3]	33.9	[1]
General and administrative expenses	'		12.2	[1],[2],[3]	11.6	[1]
Net business profits	'		17.3	[1],[2],[3]	22.3	[1]
Former Mizuho Corporate Bank, Limited Consolidated | Former Mizuho Corporate Bank, Limited Non-consolidated | Trading and others	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		135.8	[1],[2],[3]	133.3	[1]
Net noninterest income (expenses)	'		112	[1],[2],[3]	68.6	[1]
Total	'		247.8	[1],[2],[3]	201.9	[1]
General and administrative expenses	'		84.2	[1],[2],[3]	96.1	[1]
Net business profits	'		163.6	[1],[2],[3]	105.8	[1]
Former Mizuho Corporate Bank, Limited Consolidated | Former Mizuho Corporate Bank, Limited Non-consolidated | International Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		108.2	[1],[2],[3]	90.3	[1]
Net noninterest income (expenses)	'		104.7	[1],[2],[3]	86.9	[1]
Total	'		212.9	[1],[2],[3]	177.2	[1]
General and administrative expenses	'		66.6	[1],[2],[3]	60.3	[1]
Net business profits	'		146.3	[1],[2],[3]	116.9	[1]
Former Mizuho Corporate Bank, Limited Consolidated | Former Mizuho Securities Company Limited Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		'		-8.1	[1]
Net noninterest income (expenses)	'		'		151.7	[1]
Total	'		'		143.6	[1]
General and administrative expenses	'		'		192.9	[1]
Others	'		'		-0.1	[1]
Net business profits	'		'		-49.4	[1]
Former Mizuho Corporate Bank, Limited Consolidated | Mizuho Securities Company Limited Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	'		-1.8	[1],[2],[3]	'
Net noninterest income (expenses)	'		229	[1],[2],[3]	'
Total	'		227.2	[1],[2],[3]	'
General and administrative expenses	'		197.1	[1],[2],[3]	'
Net business profits	'		30.1	[1],[2],[3]	'
Mizuho Bank, Limited Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	933.8	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	407.4	[1],[2],[3],[4]	'		'
Total	1,341.20	[1],[2],[3],[4]	'		'
General and administrative expenses	711.3	[1],[2],[3],[4]	'		'
Others	-56.1	[1],[2],[3],[4]	'		'
Net business profits	573.8	[1],[2],[3],[4]	'		'
Mizuho Bank, Limited Consolidated | Others	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	133.7	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	9.2	[1],[2],[3],[4]	'		'
Total	142.9	[1],[2],[3],[4]	'		'
General and administrative expenses	52.3	[1],[2],[3],[4]	'		'
Others	-56.1	[1],[2],[3],[4]	'		'
Net business profits	34.5	[1],[2],[3],[4]	'		'
Mizuho Bank, Limited Consolidated | Mizuho Bank, Limited Non-Consolidated	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	800.1	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	398.2	[1],[2],[3],[4]	'		'
Total	1,198.30	[1],[2],[3],[4]	'		'
General and administrative expenses	659	[1],[2],[3],[4]	'		'
Net business profits	539.3	[1],[2],[3],[4]	'		'
Mizuho Bank, Limited Consolidated | Mizuho Bank, Limited Non-Consolidated | Personal Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	165	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	32.9	[1],[2],[3],[4]	'		'
Total	197.9	[1],[2],[3],[4]	'		'
General and administrative expenses	171.3	[1],[2],[3],[4]	'		'
Net business profits	26.6	[1],[2],[3],[4]	'		'
Mizuho Bank, Limited Consolidated | Mizuho Bank, Limited Non-Consolidated | Retail banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	59.8	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	34.8	[1],[2],[3],[4]	'		'
Total	94.6	[1],[2],[3],[4]	'		'
General and administrative expenses	87.8	[1],[2],[3],[4]	'		'
Net business profits	6.8	[1],[2],[3],[4]	'		'
Mizuho Bank, Limited Consolidated | Mizuho Bank, Limited Non-Consolidated | Corporate Banking (Large Corporations)	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	170.2	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	126.7	[1],[2],[3],[4]	'		'
Total	296.9	[1],[2],[3],[4]	'		'
General and administrative expenses	83.8	[1],[2],[3],[4]	'		'
Net business profits	213.1	[1],[2],[3],[4]	'		'
Mizuho Bank, Limited Consolidated | Mizuho Bank, Limited Non-Consolidated | Corporate Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	77.9	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	51.8	[1],[2],[3],[4]	'		'
Total	129.7	[1],[2],[3],[4]	'		'
General and administrative expenses	58.8	[1],[2],[3],[4]	'		'
Net business profits	70.9	[1],[2],[3],[4]	'		'
Mizuho Bank, Limited Consolidated | Mizuho Bank, Limited Non-Consolidated | Financial Institution & Public Sector Business	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	30.7	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	20.1	[1],[2],[3],[4]	'		'
Total	50.8	[1],[2],[3],[4]	'		'
General and administrative expenses	25.1	[1],[2],[3],[4]	'		'
Net business profits	25.7	[1],[2],[3],[4]	'		'
Mizuho Bank, Limited Consolidated | Mizuho Bank, Limited Non-Consolidated | Trading and others	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	167.6	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	-7.9	[1],[2],[3],[4]	'		'
Total	159.7	[1],[2],[3],[4]	'		'
General and administrative expenses	149.7	[1],[2],[3],[4]	'		'
Net business profits	10	[1],[2],[3],[4]	'		'
Mizuho Bank, Limited Consolidated | Mizuho Bank, Limited Non-Consolidated | International Banking	'		'		'
Gross profits:	'		'		'
Net interest income (expense)	128.9	[1],[2],[3],[4]	'		'
Net noninterest income (expenses)	139.8	[1],[2],[3],[4]	'		'
Total	268.7	[1],[2],[3],[4]	'		'
General and administrative expenses	82.5	[1],[2],[3],[4]	'		'
Net business profits	¥ 186.2	[1],[2],[3],[4]	'		'
[1]	As for the fiscal year ended March 31, 2012, "Others (h)", "Others (o)", and "Others (q)" include elimination of transactions between consolidated subsidiaries. As for the fiscal year ended March 31, 2013, "Others (g)", "Others (n)", and "Others (p)" include elimination of transactions between consolidated subsidiaries. As for the fiscal year ended March 31, 2014, "Others (h)" and "Others (k)" include elimination of transactions between consolidated subsidiaries.
[2]	Beginning on April 1, 2013, MHSC was turned into a directly-held subsidiary of MHFG. As for the fiscal year ended March 31, 2013, "MHSC (Consolidated) (m)" represents the performance of the former MHSC for the first three quarters and the new MHSC for the fourth quarter, while "Others (g)" includes the performance of the former MHIS for the first three quarters. As for the fiscal year ended March 31, 2014, "MHSC (Consolidated) (j)" represents the performance of the new MHSC, in light of the merger of the former MHSC and the former MHIS conducted in January 2013.
[3]	Beginning on April 1, 2013, the MHFG Group moved to a new group operational structure and realigned the reportable segments to reflect the new organizational structure. In addition, new allocation methods have been applied to the calculation of "Gross profits" and "General and administrative expenses". Figures for the fiscal year ended March 31, 2013 have been reclassified under the new allocation methods. The effect of the change of allocation methods is not significant.
[4]	As for the fiscal year ended March 31, 2014, "MHBK (Non-consolidated)" represents the sum of the performance of the former MHCB for the first quarter and the new MHBK for the second, third, and fourth quarters, while "Others (h)" includes the performance of the former MHBK for the first quarter, in light of the merger of the former MHBK and the former MHCB conducted in July 2013.

Reconciliation_of_Total_Net_Bu

Reconciliation of Total Net Business Profits Under Internal Management Reporting System to Income Loss Before Income Tax Expense Benefit Shown on Consolidated Statements of Income (Detail) (JPY ¥)	12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]	'		'		'
Net business profits	¥ 744,300,000,000	[1],[2],[3],[4]	¥ 912,200,000,000	[1],[2],[3]	¥ 719,100,000,000	[1]
U.S. GAAP adjustments	-325,400,000,000		129,200,000,000		87,200,000,000
(Provision) credit for loan losses	126,230,000,000		-139,947,000,000		23,044,000,000
Net gains (losses) related to equity investments	178,700,000,000		28,200,000,000		-90,500,000,000
Non-recurring personnel expense	-14,800,000,000		-23,500,000,000		-39,300,000,000
Gains on disposal of premises and equipment	10,460,000,000		12,411,000,000		19,924,000,000
(Provision) credit for losses on off-balance-sheet instruments	-12,095,000,000		-4,584,000,000		1,203,000,000
Others-net	18,900,000,000		-28,800,000,000		-57,800,000,000
Income before income tax expense	¥ 726,343,000,000		¥ 885,180,000,000		¥ 662,835,000,000
[1]	As for the fiscal year ended March 31, 2012, "Others (h)", "Others (o)", and "Others (q)" include elimination of transactions between consolidated subsidiaries. As for the fiscal year ended March 31, 2013, "Others (g)", "Others (n)", and "Others (p)" include elimination of transactions between consolidated subsidiaries. As for the fiscal year ended March 31, 2014, "Others (h)" and "Others (k)" include elimination of transactions between consolidated subsidiaries.
[2]	Beginning on April 1, 2013, MHSC was turned into a directly-held subsidiary of MHFG. As for the fiscal year ended March 31, 2013, "MHSC (Consolidated) (m)" represents the performance of the former MHSC for the first three quarters and the new MHSC for the fourth quarter, while "Others (g)" includes the performance of the former MHIS for the first three quarters. As for the fiscal year ended March 31, 2014, "MHSC (Consolidated) (j)" represents the performance of the new MHSC, in light of the merger of the former MHSC and the former MHIS conducted in January 2013.
[3]	Beginning on April 1, 2013, the MHFG Group moved to a new group operational structure and realigned the reportable segments to reflect the new organizational structure. In addition, new allocation methods have been applied to the calculation of "Gross profits" and "General and administrative expenses". Figures for the fiscal year ended March 31, 2013 have been reclassified under the new allocation methods. The effect of the change of allocation methods is not significant.
[4]	As for the fiscal year ended March 31, 2014, "MHBK (Non-consolidated)" represents the sum of the performance of the former MHCB for the first quarter and the new MHBK for the second, third, and fourth quarters, while "Others (h)" includes the performance of the former MHBK for the first quarter, in light of the merger of the former MHBK and the former MHCB conducted in July 2013.

Consolidated_Income_Statement_

Consolidated Income Statement and Total Assets Information by Major Geographic Area (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Segment Reporting Information [Line Items]	'		'		'
Total revenue	¥ 2,505,600	[1]	¥ 2,862,800	[1]	¥ 2,527,200	[1]
Total expenses	1,779,300	[2]	1,977,600	[2]	1,864,400	[2]
Income before income tax expense	726,343		885,180		662,835
Net income	500,235		881,156		648,957
Total assets at end of fiscal year	175,699,346		178,746,994		166,361,600
Japan	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Total revenue	1,783,900	[1]	2,190,700	[1]	1,965,700	[1]
Total expenses	1,397,300	[2]	1,668,900	[2]	1,561,200	[2]
Income before income tax expense	386,600		521,800		404,500
Net income	198,900		524,700		419,200
Total assets at end of fiscal year	124,557,700		126,768,800		124,443,600
Americas	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Total revenue	349,900	[1]	383,700	[1]	251,300	[1]
Total expenses	144,600	[2]	140,500	[2]	104,000	[2]
Income before income tax expense	205,300		243,200		147,300
Net income	189,700		252,300		131,200
Total assets at end of fiscal year	27,527,800		31,168,800		25,368,900
Europe	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Total revenue	152,900	[1]	125,800	[1]	132,000	[1]
Total expenses	96,300	[2]	48,400	[2]	102,900	[2]
Income before income tax expense	56,600		77,400		29,100
Net income	54,000		75,000		28,100
Total assets at end of fiscal year	10,784,500		10,591,200		8,868,500
Asia/Oceania excluding Japan, and others	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Total revenue	218,900	[1]	162,600	[1]	178,200	[1]
Total expenses	141,100	[2]	119,800	[2]	96,300	[2]
Income before income tax expense	77,800		42,800		81,900
Net income	57,600		29,200		70,500
Total assets at end of fiscal year	¥ 12,829,300		¥ 10,218,200		¥ 7,680,600
[1]	Total revenue is comprised of Interest and dividend income and Noninterest income.
[2]	Total expenses are comprised of Interest expense, Provision (credit) for loan losses and Noninterest expenses.

Condensed_Balance_Sheets_Paren

Condensed Balance Sheets Parent Company Only (Detail) (JPY ¥)	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
In Millions, unless otherwise specified
Assets:	'	'	'	'
Cash and due from banks	¥ 1,696,879	¥ 1,268,442	¥ 1,216,627	¥ 1,884,531
Interest-bearing deposits in other banks	19,037,527	11,215,597	'	'
Other	3,198,995	2,601,951	'	'
Total	175,699,346	178,746,994	166,361,600	'
Liabilities and shareholders' equity:	'	'	'	'
Long-term debt	9,853,941	8,802,223	'	'
Other liabilities	4,422,023	4,368,126	'	'
Shareholders' equity	6,378,470	5,728,120	'	'
Total	175,699,346	178,746,994	'	'
Parent Company	'	'	'	'
Assets:	'	'	'	'
Cash and due from banks	167	200	167	155
Interest-bearing deposits in other banks	17,103	26,165	'	'
Investments in subsidiaries and affiliated companies	7,501,486	6,962,630	'	'
Other	210,622	152,351	'	'
Total	7,729,378	7,141,346	'	'
Liabilities and shareholders' equity:	'	'	'	'
Short-term borrowings	1,061,460	1,146,995	'	'
Long-term debt	240,000	240,000	'	'
Other liabilities	49,448	26,231	'	'
Shareholders' equity	6,378,470	5,728,120	'	'
Total	¥ 7,729,378	¥ 7,141,346	'	'

Condensed_Statements_of_Income

Condensed Statements of Income Parent Company Only (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Income:	'		'		'
Total	¥ 2,505,600	[1]	¥ 2,862,800	[1]	¥ 2,527,200	[1]
Expenses:	'		'		'
Interest expense	401,565		412,851		415,959
Equity in undistributed net income of subsidiaries	27,975		-2,192		10,807
Income tax expense	226,108		4,024		13,878
Net income attributable to MHFG shareholders	498,484		875,412		656,389
Parent Company	'		'		'
Income:	'		'		'
Dividends from subsidiaries and affiliated companies	285,130		233,056		7,955
Management fees from subsidiaries	31,146		28,835		29,747
Other income	33,894		34,668		12,643
Total	350,170		296,559		50,345
Expenses:	'		'		'
Operating expenses	22,592		21,075		21,260
Interest expense	14,608		15,870		16,383
Other expense	5,724		1,207		1,431
Total	42,924		38,152		39,074
Equity in undistributed net income of subsidiaries	191,865		617,565		645,308
Income before income tax expense	499,111		875,972		656,579
Income tax expense	627		560		190
Net income attributable to MHFG shareholders	¥ 498,484		¥ 875,412		¥ 656,389
[1]	Total revenue is comprised of Interest and dividend income and Noninterest income.

Condensed_Statements_of_Cash_F

Condensed Statements of Cash Flows Parent Company Only (Detail) (JPY ¥)	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities:	'	'	'
Net income	¥ 498,484	¥ 875,412	¥ 656,389
Net cash provided by (used in) operating activities	5,951,308	-1,297,988	-1,789,431
Cash flows from investing activities:	'	'	'
Net cash provided by (used in) investing activities	417,303	-6,321,832	-1,842,893
Cash flows from financing activities:	'	'	'
Net change in short-term borrowings	-724,788	-7,251,033	-1,261,955
Proceeds from issuance of common stock	'	'	5
Purchases of treasury stock	-37,013	-7	-2,560
Dividends paid	-152,163	-152,514	-215,902
Net cash provided by (used in) financing activities	-5,972,005	7,639,859	2,965,844
Net increase (decrease) in cash and due from banks	428,437	51,815	-667,904
Cash and due from banks at beginning of fiscal year	1,268,442	1,216,627	1,884,531
Cash and due from banks at end of fiscal year	1,696,879	1,268,442	1,216,627
Parent Company	'	'	'
Cash flows from operating activities:	'	'	'
Net income	498,484	875,412	656,389
Adjustments and other	-222,940	-685,149	-644,977
Net cash provided by (used in) operating activities	275,544	190,263	11,412
Cash flows from investing activities:	'	'	'
Payments for purchases of securities of subsidiaries	'	'	-212
Net change in other investing activities	2,631	1,570	80
Net cash provided by (used in) investing activities	2,631	1,570	-132
Cash flows from financing activities:	'	'	'
Net change in short-term borrowings	-90,000	-40,000	60,000
Proceeds from issuance of common stock	'	'	146,499
Purchases of treasury stock	-37,013	-7	-2,560
Dividends paid	-152,163	-152,542	-215,937
Net change in other financing activities	968	749	730
Net cash provided by (used in) financing activities	-278,208	-191,800	-11,268
Net increase (decrease) in cash and due from banks	-33	33	12
Cash and due from banks at beginning of fiscal year	200	167	155
Cash and due from banks at end of fiscal year	¥ 167	¥ 200	¥ 167

Details_of_Redeemed_Preferred_

Details of Redeemed Preferred Securities (Detail) (Subsequent Event, Mizuho Capital Investment, Limited)	0 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2014
	USD ($)	JPY (¥)
Subsequent Event [Line Items]	'	'
Aggregate redemption amount	$850	¥ 139,500
Reason for the redemption	'Arrival of optional redemption date	'Arrival of optional redemption date