Mizuho Financial (MFG) 6-K 26 Dec 18 2018 H1 Current report (foreign) Financial data

Document and Entity Information

Document and Entity Information	6 Months Ended
	Sep. 30, 2018
Document Type	6-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	H1
Trading Symbol	MFG
Entity Registrant Name	MIZUHO FINANCIAL GROUP INC
Entity Central Index Key	1,335,730
Current Fiscal Year End Date	--03-31

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - JPY (¥) ¥ in Millions	Sep. 30, 2018	Mar. 31, 2018
Assets:
Cash and due from banks	¥ 1,566,661	¥ 1,685,835
Interest-bearing deposits in other banks	45,453,937	46,485,086
Call loans and funds sold	420,017	720,461
Receivables under resale agreements	10,274,835	8,080,927
Receivables under securities borrowing transactions	2,709,641	4,408,508
Trading account assets	23,420,966	24,302,543
Investments (Note 3):
Available-for-sale securities (including assets pledged that secured parties are permitted to sell or repledge of ¥932,302 million at March 31, 2018 and ¥1,168,516 million at September 30, 2018)	20,471,615	23,665,628
Held-to-maturity securities (including assets pledged that secured parties are permitted to sell or repledge of ¥677,046 million at March 31, 2018 and ¥595,220 million at September 30, 2018)	2,137,011	2,517,551
Equity securities	4,769,603
Other investments	342,754	585,896
Loans (Notes 4 and 5)	84,830,248	83,514,644
Allowance for loan losses	(274,489)	(309,902)
Loans, net of allowance	84,555,759	83,204,742
Premises and equipment-net	2,013,006	2,116,184
Due from customers on acceptances	263,890	212,596
Accrued income	325,466	301,332
Goodwill	95,150	95,184
Intangible assets	79,707	84,447
Deferred tax assets	52,261	57,088
All other assets	5,226,525	5,731,634
Total	204,178,804	204,255,642
Liabilities and equity:
Noninterest-bearing deposits	23,051,185	21,068,569
Interest-bearing deposits	83,680,943	91,206,963
Noninterest-bearing deposits	1,796,296	2,257,350
Interest-bearing deposits	25,250,812	22,351,124
Due to trust accounts	3,965,632	3,992,544
Call money and funds purchased	5,736,054	2,105,294
Payables under repurchase agreements (Note 19)	17,488,422	16,656,930
Payables under securities lending transactions (Note 19)	2,112,335	1,832,870
Other short-term borrowings	1,753,964	1,688,018
Trading account liabilities	9,744,238	13,115,270
Bank acceptances outstanding	263,890	212,596
Income taxes payable	98,597	64,501
Deferred tax liabilities	238,656	306,203
Accrued expenses	237,720	232,885
Long-term debt	13,533,141	12,955,230
All other liabilities	5,395,082	4,705,595
Total	194,346,967	194,751,942
Commitments and contingencies (Note 14)
MHFG shareholders' equity:
Common stock (Note 7)-no par value, authorized 48,000,000,000 shares at March 31, 2018 and September 30, 2018, and issued 25,389,644,945 shares at March 31, 2018, and 25,392,498,945 shares at September 30, 2018	5,828,762	5,826,383
Retained earnings	3,033,546	1,306,141
Accumulated other comprehensive income, net of tax (Note 8)	187,915	1,741,894
Less: Treasury stock, at cost-Common stock 24,829,446 shares at March 31, 2018, and 34,314,755 shares at September 30, 2018	(7,889)	(5,997)
Total MHFG shareholders' equity	9,042,334	8,868,421
Noncontrolling interests	789,503	635,279
Total equity	9,831,837	9,503,700
Total liabilities and equity	204,178,804	204,255,642
Consolidated VIEs
Assets:
Cash and due from banks	11,584	31,435
Interest-bearing deposits in other banks	38,202	95,048
Trading account assets	2,767,980	2,558,186
Investments (Note 3):
Investments	52,333	48,565
Loans, net of allowance	2,190,319	2,323,081
All other assets	901,682	811,453
Total	5,962,100	5,867,768
Liabilities and equity:
Other short-term borrowings	33,461	31,392
Trading account liabilities	1,919	22
Long-term debt	367,801	419,649
All other liabilities	1,436,709	1,305,640
Total	¥ 1,839,890	¥ 1,756,703

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - JPY (¥) ¥ in Millions	Sep. 30, 2018	Mar. 31, 2018
Trading account assets, assets pledged that secured parties are permitted to sell or repledge	¥ 5,983,056	¥ 4,897,190
Available-for-sale securities, assets pledged that secured parties are permitted to sell or repledge	1,168,516	932,302
Held-to-maturity securities, assets pledged that secured parties are permitted to sell or repledge	595,220	677,046
Long-term debt, liabilities accounted for at fair value	¥ 2,380,034	¥ 1,955,636
Common stock, par value	¥ 0	¥ 0
Common stock, authorized	48,000,000,000	48,000,000,000
Common stock, issued	25,392,498,945	25,389,644,945
Treasury stock, shares	34,314,755	24,829,446

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Interest and dividend income:
Loans, including fees		¥ 655,981	¥ 537,959
Investments:
Interest		64,780	37,909
Dividends		43,936	41,781
Trading account assets		113,687	99,569
Call loans and funds sold		2,121	2,829
Receivables under resale agreements and securities borrowing transactions		106,246	66,572
Deposits in other banks		55,039	52,806
Total interest and dividend income		1,041,790	839,425
Interest expense:
Deposits		270,721	182,020
Trading account liabilities		24,251	19,371
Call money and funds purchased		4,914	1,855
Payables under repurchase agreements and securities lending transactions		166,042	106,357
Other short-term borrowings		14,531	6,645
Long-term debt		106,608	97,057
Total interest expense		587,067	413,305
Net interest income		454,723	426,120
Provision (credit) for loan losses (Note 5)		(13,280)	(117,962)
Net interest income after provision (credit) for loan losses		468,003	544,082
Noninterest income (Note 16):
Fee and commission income		413,727	401,231
Foreign exchange gains (losses)-net	[1]	44,718	50,765
Trading account gains (losses)-net	[2]	64,956	235,339
Investment gains (losses)-net (Note 2):
Debt securities	[1]	2,485	16,099
Equity securities	[1]	306,788	109,390
Equity in earnings (losses) of equity method investees-net	[1]	22,627	10,389
Gains on disposal of premises and equipment	[1]	4,305	4,567
Other noninterest income	[2]	48,950	33,158
Total noninterest income		908,556	860,938
Noninterest expenses:
Salaries and employee benefits		342,686	341,853
General and administrative expenses		359,358	280,176
Occupancy expenses		93,921	96,340
Fee and commission expenses		98,779	98,298
Provision (credit) for losses on off-balance-sheet instruments		(9,877)	(4,191)
Other noninterest expenses		74,042	79,681
Total noninterest expenses		958,909	892,157
Income before income tax expense		417,650	512,863
Income tax expense (Note 11)		85,705	119,333
Net income		331,945	393,530
Less: Net income attributable to noncontrolling interests		46,675	20,981
Net income attributable to MHFG shareholders		¥ 285,270	¥ 372,549
Earnings per common share (Note 10):
Basic net income per common share		¥ 11.25	¥ 14.69
Diluted net income per common share		11.25	14.68
Dividends per common share		¥ 3.75	¥ 3.75
[1]	These amounts are revenues from contracts that do not meet the scope of ASC 606.
[2]	Part of these amounts are considered to be revenues from contracts that are within the scope of ASC 606.

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Net income	¥ 331,945	¥ 393,530
Other comprehensive income (loss), net of tax	(19,030)	165,077
Total comprehensive income	312,915	558,607
Less: Total comprehensive income attributable to noncontrolling interests	46,482	21,374
Total comprehensive income attributable to MHFG shareholders	¥ 266,433	¥ 537,233

CONSOLIDATED STATEMENTS OF EQUI

CONSOLIDATED STATEMENTS OF EQUITY - JPY (¥) ¥ in Millions	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock	Parent	Noncontrolling Interest
Balance at beginning of period at Mar. 31, 2017		¥ 5,826,149	¥ 918,894	¥ 1,521,163	¥ (4,849)		¥ 510,700
Issuance of new shares of common stock due to exercise of stock acquisition rights		546
Purchases of treasury stock					(2,447)
Balance at beginning of period, adjusted at Mar. 31, 2017			918,894	1,521,163			510,700
Performance-based stock compensation program		(815)
Disposal of treasury stock					821
Effect of other increase (decrease) in noncontrolling interests							(27,629)
Net income attributable to MHFG shareholders	¥ 372,549		372,549
Change during period	165,077			164,684
Other		79
Dividends paid to noncontrolling interests							(5,284)
Dividends declared			(95,174)
Net income attributable to noncontrolling interests	(20,981)						20,981
Other							393
Balance at end of fiscal year at Sep. 30, 2017	9,200,761	5,825,959	1,196,269	1,685,847	(6,475)	¥ 8,701,600	499,161
Balance at beginning of period at Mar. 31, 2018	9,503,700	5,826,383	1,306,141	1,741,894	(5,997)		635,279
Cumulative effect of change in accounting principles at Mar. 31, 2018			1,537,322	(1,535,142)			(616)
Issuance of new shares of common stock due to exercise of stock acquisition rights		438
Purchases of treasury stock					(2,857)
Balance at beginning of period, adjusted at Mar. 31, 2018			2,843,463	206,752			634,663
Performance-based stock compensation program		(1,053)
Disposal of treasury stock					965
Effect of other increase (decrease) in noncontrolling interests							117,649
Net income attributable to MHFG shareholders	285,270		285,270
Change during period	(19,030)			(18,837)
Other		2,994
Dividends paid to noncontrolling interests							(9,291)
Dividends declared			(95,187)
Net income attributable to noncontrolling interests	(46,675)						46,675
Other							(193)
Balance at end of fiscal year at Sep. 30, 2018	¥ 9,831,837	¥ 5,828,762	¥ 3,033,546	¥ 187,915	¥ (7,889)	¥ 9,042,334	¥ 789,503

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income		¥ 331,945	¥ 393,530
Less: Net income attributable to noncontrolling interests		46,675	20,981
Net income attributable to MHFG shareholders		285,270	372,549
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization		162,433	90,064
Provision (credit) for loan losses		(13,280)	(117,962)
Investment losses (gains)-net		(309,273)	(125,489)
Equity in losses (earnings) of equity method investees-net	[1]	(22,627)	(10,389)
Foreign exchange losses (gains)-net		288,705	19,441
Deferred income tax expense (benefit)		(28,961)	20,095
Net change in trading account assets		935,498	(1,166,688)
Net change in trading account liabilities		(3,437,556)	(766,841)
Net change in loans held for sale		44,830	(2,970)
Net change in accrued income		(20,565)	(13,400)
Net change in accrued expenses		34,490	(5,735)
Other-net		180,989	(817,607)
Net cash used in operating activities		(1,900,047)	(2,524,932)
Cash flows from investing activities:
Proceeds from sales of investments		13,698,688	16,390,837
Proceeds from maturities of investments		8,494,080	9,274,406
Purchases of investments		(21,707,934)	(24,412,985)
Proceeds from sales of loans		153,856	180,179
Net change in loans		(625,828)	(1,371,811)
Net change in call loans and funds sold, and receivables under resale agreements and securities borrowing transactions		165,558	(316,202)
Proceeds from sales of premises and equipment		6,764	18,524
Purchases of premises and equipment		(63,855)	(157,322)
Proceeds from sales of investments in subsidiaries (affecting the scope of consolidation)			948
Net cash provided by (used in) investing activities		121,329	(393,426)
Cash flows from financing activities:
Net change in deposits		(3,964,784)	5,267,913
Net change in call money and funds purchased, and payables under repurchase agreements and securities lending transactions		3,951,434	2,621,193
Net change in due to trust accounts		(26,912)	(123,732)
Net change in other short-term borrowings		10,760	(545,814)
Proceeds from issuance of long-term debt		1,286,316	1,377,698
Repayment of long-term debt		(984,642)	(1,835,014)
Proceeds from noncontrolling interests		140,068	927
Payments to noncontrolling interests			(11,883)
Proceeds from issuance of common stock		3	3
Proceeds from sales of treasury stock		933
Purchases of treasury stock		(2,102)	(1,605)
Dividends paid		(95,163)	(95,139)
Dividends paid to noncontrolling interests		(9,291)	(5,284)
Net cash provided by financing activities		306,620	6,649,263
Effect of exchange rate changes on cash and cash equivalents		321,775	79,664
Net increase (decrease) in cash and cash equivalents		(1,150,323)	3,810,569
Cash and cash equivalents at beginning of period		48,170,921	47,586,971
Cash and cash equivalents at end of period		47,020,598	51,397,540
Noncash investing activities:
Investment in capital leases		¥ 501	¥ 1,807
[1]	These amounts are revenues from contracts that do not meet the scope of ASC 606.

Basis of presentation

Basis of presentation	6 Months Ended
	Sep. 30, 2018
Basis of presentation	1. 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. For a discussion of the Group’s segment information, see Note 20 “Business segment information”. MHFG and its domestic subsidiaries as well as its foreign subsidiaries maintain their accounting records in accordance with the accounting standards of Japan and those standards of the countries in which they are domiciled. Certain adjustments and reclassifications have been incorporated in the accompanying consolidated financial statements to conform them to 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 interim financial reporting period ends on September 30 and certain subsidiaries’ interim financial reporting periods end on June 30. When determining whether to consolidate investee entities, the MHFG Group performed an analysis of the facts and circumstances of the particular relationships between the MHFG Group and the investee entities as well as the 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 in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 810, “Consolidation” (“ASC 810”). All significant intercompany transactions and balances have been eliminated upon consolidation. The MHFG Group accounts for investments in entities over which it has significant influence by 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 Equity in earnings (losses) of equity method investees—net. Certain comparative amounts for the prior period have been reclassified in order to conform to the current year’s presentation. The unaudited consolidated financial statements should be read in conjunction with the audited financial statements and related notes thereto included in the annual financial statements for the fiscal year ended March 31, 2018. Certain financial information that is normally included in annual financial statements prepared in accordance with U.S. GAAP, but is not required for interim reporting purposes, has been condensed or omitted. 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 Definition of cash and cash equivalents For purposes of the consolidated statements of cash flows, Cash and cash equivalents consists of Cash and due from banks and Interest-bearing deposits in other banks. Cash deposited with central banks that must be maintained to meet minimum regulatory requirements is classified as restricted cash and included in Cash and cash equivalents. For more information on restricted cash, see Note 9 “Pledged assets and collateral” of MHFG’s Form 20-F for the fiscal year ended March 31, 2018. The MHFG Group adopted ASU No.2016-18, “Statement of Cash Flows (Topic230)—Restricted Cash” (“ASU No.2016-18”) using the retrospective approach. In accordance with the adoption, the MHFG Group changed the definition of cash and cash equivalents as mentioned above. As a result of the adoption of the ASU No.2016-18, the MHFG Group recorded a decrease of ¥3,415 million in Net cash provided by (used in) operating activities for the six months ended September 30, 2017, and an increase of ¥3,932,027 million in Net cash provided by (used in) investing activities for the six months ended September 30, 2017. Deconsolidation of TCSB In March 2018, Trust & Custody Services Bank, Ltd. (“TCSB”), MHFG’s subsidiary, and Japan Trustee Services Bank, Ltd. (“JTSB”) entered into a management integration agreement. Based on the agreement, TCSB and JTSB incorporated a holding company, JTC Holdings, Ltd. (“JTC Holdings”) through joint share transfer on October 1, 2018, and became wholly-owned subsidiaries of JTC Holdings on that date. Starting October 1, 2018, MHFG will no longer consolidate TCSB, which had approximately ¥9 trillion in total assets as of September 30, 2018. However, MHFG will maintain an investment in JTC Holdings and will account for this investment using the equity method of accounting.

Recently issued accounting pron

Recently issued accounting pronouncements	6 Months Ended
	Sep. 30, 2018
Recently issued accounting pronouncements	2. Recently issued accounting pronouncements Recently adopted accounting pronouncements In May 2014, the FASB issued ASU No.2014-09, No.2014-09”). No.2014-09 No.2014-09 In January 2016, the FASB issued ASU No.2016-01, “Financial Instruments—Overall (Subtopic 825-10)—Recognition and Measurement of Financial Assets and Financial Liabilities” (“ASU No.2016-01”). The ASU requires equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The ASU also requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. The ASU is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, and should be applied using a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption, which increased Retained earnings of ¥1,542 billion, net of tax, including any stranded tax amounts from prior periods, on April 1, 2018. The impact of the adoption primarily resulted in a cumulative-effect adjustment out of Accumulated other comprehensive income (“AOCI”) to Retained earnings related to the equity investments, which increased Retained earnings of ¥1,527 billion, net of tax, including any stranded tax amounts from prior periods, on April 1, 2018. Before the adoption of ASU No.2016-01, marketable equity securities for which the MHFG Group elected the fair value option were reported as Trading account assets, other marketable equity securities (except those outside the scope of previous ASC 320, “Investments—Debt and Equity Securities” (“Previous ASC 320”)) were reported as Available-for-sale securities, and other equity interests which primarily consist of non-marketable equity securities were reported as Other investments. After the adoption of ASU No.2016-01, all of these securities are reported as Equity securities. In connection with the adoption of ASU No.2016-01, Investments gains (losses)—net of Equity securities and Debt securities are presented separately in the Group’s consolidated results of operations. The amounts for the prior periods have been reclassified in order to conform to the current year’s presentation. For additional information, see Note 3 “Investments”, Note 8 “Accumulated other comprehensive income”, Note 13 “Derivative financial instruments” and Note 17 “Fair value”. The impact of the adoption resulted in a cumulative-effect adjustment out of Retained earnings to AOCI related to the liabilities for which the fair value option was elected, which increased Retained earnings of ¥10 billion, net of tax, on April 1, 2018. For additional information, see Note 8 “Accumulated other comprehensive income”, Note 11 “Income taxes” and Note 17 “Fair value”. In October 2016, the FASB issued ASU No.2016-16, No.2016-16”). No. 2016-16 In May 2017, the FASB issued ASU No.2017-09, No.2017-09”). No. 2017-09 Accounting pronouncements issued but not yet effective In February 2016, the FASB issued ASU No.2016-02, No.2016-02”). right-of-use right-of-use 20-F In June 2016, the FASB issued ASU No.2016-13, No.2016-13”). available-for-sale No.2016-13 In January 2017, the FASB issued ASU No.2017-04, No.2017-04”). No. 2017-04 In August 2017, the FASB issued ASU No.2017-12, No.2017-12 In February 2018, the FASB issued ASU No.2018-02, No.2018-02”). No. 2018-02 In August 2018, the FASB issued ASU No.2018-13, No.2018-13”). No.2018-13 In August 2018, the FASB issued ASU No.2018-14, “Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20)—Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans” (“ASU No.2018-14”). The amendments in this update remove disclosures that no longer are considered cost beneficial, clarify the specific requirements of disclosures, and add disclosure requirements identified as relevant. Mainly, the ASU removes the disclosure requirement of the amounts in accumulated other comprehensive income expected to be recognized as components of net periodic benefit cost over the next fiscal year, and adds the disclosure requirement of the weighted-average interest crediting rates for cash balance plans and other plans with promised interest crediting rates. The ASU is effective for fiscal years ending after December 15, 2020, and should be applied on a retrospective basis to all periods presented. Early application is permitted for all entities. The MHFG Group is currently evaluating the potential impact that the adoption of ASU No.2018-14 will have on its consolidated results of operations and financial condition. In October 2018, the FASB issued ASU No.2018-16, “Derivatives and Hedging (Topic 815)—Inclusion of the Secured Overnight Financing Rate (“SOFR”) Overnight Index Swap (“OIS”) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes” (“ASU No.2018-16”). The ASU permits use of the OIS rate based on SOFR as a U.S. benchmark interest rate for hedge accounting purposes under Topic 815 in addition to the interest rates on direct Treasury obligations of the U.S. government (“UST”), the London Interbank Offered Rate (“LIBOR”) swap rate, the OIS rate based on the Federal Funds Effective Rate, and the Securities Industry and Financial Markets Association (“SIFMA”) Municipal Swap Rate. The amendments in ASU No.2018-16 are required to be adopted concurrently with the amendments in ASU No.2017-12, and should be applied on a prospective basis for qualifying new or redesignated hedging relationships entered into on or after the date of adoption. Early application is permitted, including adoption in any interim period. The MHFG Group does not expect that the adoption of ASU No.2018-16 will have a material impact on its consolidated results of operations or financial condition. In October 2018, the FASB issued ASU No.2018-17, No.2018-17”). No.2018-17

Investments

Investments	6 Months Ended
	Sep. 30, 2018
Investments	3. Investments Available-for-sale held-to-maturity The amortized cost, gross unrealized gains and losses, and fair value of available-for-sale held-to-maturity Amortized cost Gross unrealized Gross unrealized Fair value (in millions of yen) March 31, 2018 Available-for-sale Debt securities: Japanese government bonds 13,334,619 7,332 9,656 13,332,295 Japanese local government bonds 236,711 2,903 280 239,334 U.S. Treasury bonds and federal agency securities 689,297 109 3,557 685,849 Other foreign government bonds 1,057,852 1,043 1,102 1,057,793 Agency mortgage-backed securities (1) 882,686 13,356 7,628 888,414 Residential mortgage-backed securities 117,870 1,264 281 118,853 Commercial mortgage-backed securities 437,115 4,132 323 440,924 Japanese corporate bonds and other debt securities (2) 1,950,947 40,290 1,410 1,989,827 Foreign corporate bonds and other debt securities (3) 879,506 1,927 2,082 879,351 Equity securities (marketable) (4) 1,595,106 2,449,173 11,291 4,032,988 Total 21,181,709 2,521,529 37,610 23,665,628 Held-to-maturity Debt securities: Japanese government bonds 1,959,910 24,472 — 1,984,382 Agency mortgage-backed securities (5) 557,641 — 20,177 537,464 Total 2,517,551 24,472 20,177 2,521,846 September 30, 2018 Available-for-sale Debt securities: Japanese government bonds 13,468,933 3,947 21,693 13,451,187 Japanese local government bonds 240,193 914 652 240,455 U.S. Treasury bonds and federal agency securities 1,138,917 78 5,204 1,133,791 Other foreign government bonds 1,244,490 557 1,669 1,243,378 Agency mortgage-backed securities (1) 871,031 9,984 10,008 871,007 Residential mortgage-backed securities 108,963 908 434 109,437 Commercial mortgage-backed securities 465,251 3,641 298 468,594 Japanese corporate bonds and other debt securities (2) 2,010,207 30,992 2,356 2,038,843 Foreign corporate bonds and other debt securities (3) 913,328 2,580 985 914,923 Equity securities (marketable) (4) — — — — Total 20,461,313 53,601 43,299 20,471,615 Held-to-maturity Debt securities: Japanese government bonds 1,599,900 19,418 — 1,619,318 Agency mortgage-backed securities (5) 537,111 — 24,153 512,958 Total 2,137,011 19,418 24,153 2,132,276 Notes: (1) Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥742,565 million and ¥145,849 million, respectively, at March 31, 2018, and ¥728,836 million and ¥142,171 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Government National Mortgage Association (“Ginnie Mae”) securities, which are guaranteed by the United States government. (2) Other debt securities presented in this line primarily consist of Japanese negotiable certificates of deposit (“NCDs”), of which the total fair values were ¥106,101 million at March 31, 2018, and ¥104,775 million at September 30, 2018. (3) Other debt securities presented in this line primarily consist of Foreign NCDs and asset-backed securities (“ABS”), of which the total fair values were ¥313,164 million at March 31, 2018, and ¥342,999 million at September 30, 2018. (4) The MHFG Group adopted ASU No.2016-01 available-for-sale (5) All Agency mortgage-backed securities presented in this line are Ginnie Mae securities. Contractual maturities The amortized cost and fair value of available-for-sale held-to-maturity Amortized cost Due in one Due after one Due after five Due after Total (in millions of yen) Available-for-sale Debt securities: Japanese government bonds 8,373,572 3,722,338 1,063,748 309,275 13,468,933 Japanese local government bonds 29,530 143,921 61,579 5,163 240,193 U.S. Treasury bonds and federal agency securities 1,033,650 — 105,267 — 1,138,917 Other foreign government bonds 970,819 258,152 12,602 2,917 1,244,490 Agency mortgage-backed securities — — — 871,031 871,031 Residential mortgage-backed securities — — — 108,963 108,963 Commercial mortgage-backed securities 1,852 178,690 212,459 72,250 465,251 Japanese corporate bonds and other debt securities 407,643 989,938 427,553 185,073 2,010,207 Foreign corporate bonds and other debt securities 514,374 330,725 65,459 2,770 913,328 Total 11,331,440 5,623,764 1,948,667 1,557,442 20,461,313 Held-to-maturity Debt securities: Japanese government bonds 960,044 479,868 159,988 — 1,599,900 Agency mortgage-backed securities — — — 537,111 537,111 Total 960,044 479,868 159,988 537,111 2,137,011 Fair value Due in one Due after one Due after five Due after Total (in millions of yen) Available-for-sale Debt securities: Japanese government bonds 8,372,894 3,722,825 1,054,008 301,460 13,451,187 Japanese local government bonds 29,558 144,269 61,492 5,136 240,455 U.S. Treasury bonds and federal agency securities 1,033,135 — 100,656 — 1,133,791 Other foreign government bonds 970,233 257,751 12,489 2,905 1,243,378 Agency mortgage-backed securities — — — 871,007 871,007 Residential mortgage-backed securities — — — 109,437 109,437 Commercial mortgage-backed securities 1,852 179,517 214,475 72,750 468,594 Japanese corporate bonds and other debt securities 431,664 991,020 428,321 187,838 2,038,843 Foreign corporate bonds and other debt securities 514,166 332,225 65,762 2,770 914,923 Total 11,353,502 5,627,607 1,937,203 1,553,303 20,471,615 Held-to-maturity Debt securities: Japanese government bonds 961,712 492,560 165,046 — 1,619,318 Agency mortgage-backed securities — — — 512,958 512,958 Total 961,712 492,560 165,046 512,958 2,132,276 Other-than-temporary impairment The MHFG Group performs periodic reviews to identify impaired securities in accordance with ASC 320, “Investments—Debt Securities” (“ASC 320”). For debt securities, in the cases where the MHFG Group has the intent to sell a debt security or more likely than not will be required to sell a debt security before the recovery of its amortized cost basis, the full amount of an other-than-temporary impairment loss is recognized immediately through earnings. In other cases, the MHFG Group evaluates expected cash flows to be received and determines if a credit loss exists, and if so, the amount of an other-than-temporary impairment related to the credit loss is recognized in earnings, while the remaining decline in fair value is recognized in other comprehensive income, net of applicable taxes. Effective April 1, 2018, the available-for-sale No.2016-01, The following table shows the other-than-temporary impairment losses on available-for-sale held-to-maturity Six months ended September 30, 2017 2018 (in millions of yen) Available-for-sale Debt securities 1,000 213 Equity securities (Note) 2,521 — Total 3,521 213 Note: Effective April 1, 2018, the available-for-sale For the six months ended September 30, 2018, the other-than-temporary impairment losses on debt securities were attributable to the decline in the fair value of certain Japanese corporate bonds in respect of which the MHFG Group determined credit losses existed. In accordance with ASC 320, the other-than-temporary impairment on these securities was recognized in earnings. The total other-than-temporary impairment met the criteria to be immediately recorded in earnings and no portion was recognized in other comprehensive income. Continuous unrealized loss position The following table shows 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, 2018 and September 30, 2018: Less than 12 months 12 months or more Total Fair Gross Fair Gross Fair Gross (in millions of yen) March 31, 2018 Available-for-sale Debt securities: Japanese government bonds 8,052,820 3,716 2,868,078 5,940 10,920,898 9,656 Japanese local government bonds 28,827 139 58,998 141 87,825 280 U.S. Treasury bonds and federal agency securities 515,005 3,557 — — 515,005 3,557 Other foreign government bonds 419,648 1,030 68,359 72 488,007 1,102 Agency mortgage-backed securities (1) 45,434 1,116 188,326 6,512 233,760 7,628 Residential mortgage-backed securities 11,336 14 16,129 267 27,465 281 Commercial mortgage-backed securities 68,723 242 7,835 81 76,558 323 Japanese corporate bonds and other debt securities 563,831 933 403,069 477 966,900 1,410 Foreign corporate bonds and other debt securities 358,410 888 87,472 1,194 445,882 2,082 Equity securities (marketable) (2) 338,243 11,249 366 42 338,609 11,291 Total 10,402,277 22,884 3,698,632 14,726 14,100,909 37,610 Held-to-maturity Debt securities: Agency mortgage-backed securities (3) 30,589 766 506,875 19,411 537,464 20,177 Total 30,589 766 506,875 19,411 537,464 20,177 September 30, 2018 Available-for-sale Debt securities: Japanese government bonds 6,763,194 13,798 3,243,600 7,895 10,006,794 21,693 Japanese local government bonds 92,616 329 83,400 323 176,016 652 U.S. Treasury bonds and federal agency securities 961,157 2,107 52,378 3,097 1,013,535 5,204 Other foreign government bonds 704,626 1,023 46,274 646 750,900 1,669 Agency mortgage-backed securities (1) 151,610 782 204,959 9,226 356,569 10,008 Residential mortgage-backed securities 26,351 151 24,883 283 51,234 434 Commercial mortgage-backed securities 44,603 118 42,526 180 87,129 298 Japanese corporate bonds and other debt securities 497,300 1,767 599,554 589 1,096,854 2,356 Foreign corporate bonds and other debt securities 222,267 400 102,586 585 324,853 985 Equity securities (marketable) (2) — — — — — — Total 9,463,724 20,475 4,400,160 22,824 13,863,884 43,299 Held-to-maturity Debt securities: Agency mortgage-backed securities (3) 22,319 827 490,639 23,326 512,958 24,153 Total 22,319 827 490,639 23,326 512,958 24,153 Notes: (1) Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥88,017 million and ¥145,743 million, respectively, at March 31, 2018, and ¥214,480 million and ¥142,089 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Ginnie Mae securities, which are guaranteed by the United States government. (2) The MHFG Group adopted ASU No.2016-01 (3) All Agency mortgage-backed securities presented in this line are Ginnie Mae securities. At September 30, 2018, the MHFG Group did not intend to sell the debt securities in an unrealized loss position and it was not more likely than not that the MHFG Group would be required to sell them before the recovery of their amortized cost bases. For Japanese government bonds, U.S. Treasury bonds and federal agency securities and Agency mortgage-backed securities, their entire amortized cost bases were expected to be recovered since the unrealized losses had not resulted from credit deterioration, but primarily from changes in interest rates. For the debt securities other than those described above, including Japanese corporate bonds with similar credit risks as the other-than-temporarily impaired securities, the MHFG Group determined that their entire amortized cost bases were expected to be recovered, after considering various factors such as the extent to which their fair values were below their amortized cost bases, the external and/or internal ratings and the present values of cash flows expected to be collected. Based on the aforementioned evaluation, except for the securities for which credit losses have been recognized in income, the MHFG Group determined that the debt securities in an unrealized loss position were not considered other-than-temporarily impaired. Realized gains and losses The following table shows the realized gains and losses on sales of available-for-sale available-for-sale Six months ended September 30, 2017 2018 (in millions of yen) Gross realized gains 127,360 9,955 (Note) Gross realized losses (10,020 ) (8,497 ) (Note) Net realized gains (losses) on sales of available-for-sale 117,340 1,458 (Note) Note: Effective April 1, 2018, the available-for-sale Other investments The following table summarizes the composition of Other investments at March 31, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 (in millions of yen) Equity method investments 280,666 301,524 Investments held by consolidated investment companies 37,735 41,230 Other equity interests 267,495 — (Note) Total 585,896 342,754 Note: In connection with the adoption of ASU No.2016-01, other equity interests are disclosed as Equity securities. See Note 2 “Recently issued accounting pronouncements” for further details. 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. Such investments included marketable equity securities with carrying values of ¥152,445 million and ¥167,316 million, at March 31, 2018 and September 30, 2018, respectively. The aggregate market values of these marketable equity securities were ¥324,239 million and ¥312,520 million, respectively. The majority of the aggregate market values of these marketable equity securities are related to Orient Corporation, of which the MHFG Group’s proportionate share of the total outstanding common stock was 49.0% as of September 30, 2018. 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 Other equity interests Other equity interests primarily consist of non-marketable Equity securities Equity securities include securities which have readily determinable fair values, securities which qualify for the practical expedient to estimate fair value using the net asset value per share (or its equivalent), and securities which are without readily determinable fair values. Equity securities which have readily determinable fair values mainly consist of common stock of Japanese listed companies. Equity securities without readily determinable fair values include non-marketable Net gains and losses The following table shows the details of the net gains and losses on Equity securities for the six months ended September 30, 2018: Six months ended 2018 (in millions of yen) Net gains and losses recognized during the period on equity securities 306,788 Less: Net gains and losses recognized during the period on equity securities sold during the period 116,308 Unrealized gains and losses recognized during the reporting period on equity securities still held at the reporting period 190,480 Equity securities without readily determinable fair values The following table shows the details of Equity securities without readily determinable fair values, for which the measurement alternative is used, for the six months ended September 30, 2018: Six months ended 2018 (in millions of yen) Carrying amounts at the end of the period 231,810 Downward adjustments and impairments: During the period 976 Cumulative 976 Upward adjustments: During the period 1,837 Cumulative 1,837 The MHFG Group elected to measure all equity securities without readily determinable fair values, which do not qualify for the practical expedient to estimate fair value, using the measurement alternative, which is made on an instrument-by-instrument

Loans

Loans	6 Months Ended
	Sep. 30, 2018
Loans	4. Loans The table below presents loans outstanding by domicile and industry of borrower at March 31, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 (in millions of yen) Domestic: Manufacturing 8,156,341 8,469,440 Construction and real estate 8,101,668 8,475,834 Services 5,024,018 5,288,571 Wholesale and retail 5,112,673 5,168,408 Transportation and communications 3,564,869 3,710,990 Banks and other financial institutions 4,471,423 4,455,338 Government and public institutions 8,882,125 5,776,149 Other industries (Note) 5,018,387 5,059,891 Individuals: Mortgage loans 9,445,286 9,191,280 Other 883,724 867,192 Total domestic 58,660,514 56,463,093 Foreign: Commercial and industrial 17,195,159 19,322,908 Banks and other financial institutions 7,465,140 8,527,586 Government and public institutions 302,891 625,263 Other 37,636 41,699 Total foreign 25,000,826 28,517,456 Total 83,661,340 84,980,549 Less: Unearned income and deferred loan fees—net 146,696 150,301 Total loans before allowance for loan losses 83,514,644 84,830,248 Note: Other industries of Domestic includes trade receivables and lease receivables of consolidated VIEs. Net losses on sales of loans were ¥3,739 million and ¥1,060 million, including unrealized losses related to recording loans held for sale at the lower of cost or fair value for the six months ended September 30, 2017 and 2018, respectively. The gains and losses on sales of loans are recorded in Other noninterest income and expenses, 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 loans 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 groups of small balance, homogeneous 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 policies and procedures. The table below presents the MHFG Group’s definition of obligor ratings used by Mizuho Bank, Ltd. (“MHBK”) and Mizuho Trust & Banking Co., Ltd. (“MHTB”): Obligor category (1)(2) 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 economic environmental changes is low. Watch E1 Obligors that require observation going forward because of either minor concerns regarding their financial position, or their 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 to make principal or interest payments, or problems with their financial position as a result of their weak or unstable business conditions. 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. Notes: (1) Special attention obligors are watch obligors with debt in troubled debt restructuring (“TDR”) or 90 days or more delinquent debt. Loans to such obligors are considered impaired. (2) The Group classifies loans to special attention, intensive control, substantially bankrupt and bankrupt obligors as impaired loans. The table below presents credit quality information of loans based on the MHFG Group’s internal rating system at March 31, 2018 and September 30, 2018: Normal obligors Watch obligors (1) Corporate Retail (2) Other (3) Corporate Retail (2) Other (3) Impaired Total (in millions of yen) March 31, 2018 Domestic: Manufacturing 7,705,495 77,947 23,343 197,465 9,775 246 142,070 8,156,341 Construction and real estate 7,317,972 541,778 13,332 172,287 15,466 — 40,833 8,101,668 Services 4,535,793 172,045 141,718 95,223 21,109 55 58,075 5,024,018 Wholesale and retail 4,636,236 177,965 17,305 121,832 27,975 476 130,884 5,112,673 Transportation and communications 3,414,781 76,532 1,774 35,339 8,916 — 27,527 3,564,869 Banks and other financial institutions 4,244,101 1,640 196,431 16,716 194 — 12,341 4,471,423 Government and public institutions 3,010,708 — 5,871,417 — — — — 8,882,125 Other industries (4) 2,716,502 3,536 2,170,442 2,708 259 121,201 3,739 5,018,387 Individuals 222,410 9,822,244 88,044 23,491 81,550 1,109 90,162 10,329,010 Total domestic 37,803,998 10,873,687 8,523,806 665,061 165,244 123,087 505,631 58,660,514 Foreign: Commercial and industrial 14,192,930 209 2,432,189 398,231 — 64,950 106,650 17,195,159 Banks and other financial institutions 6,949,036 — 487,978 28,126 — — — 7,465,140 Government and public institutions 301,072 — — — — — 1,819 302,891 Other 1,906 9,245 23,730 242 6 1,347 1,160 37,636 Total foreign 21,444,944 9,454 2,943,897 426,599 6 66,297 109,629 25,000,826 Total 59,248,942 10,883,141 11,467,703 1,091,660 165,250 189,384 615,260 83,661,340 September 30, 2018 Domestic: Manufacturing 8,130,139 72,651 15,714 124,530 8,305 522 117,579 8,469,440 Construction and real estate 7,709,697 522,815 10,358 178,226 15,083 — 39,655 8,475,834 Services 4,731,189 168,384 206,848 91,898 18,863 — 71,389 5,288,571 Wholesale and retail 4,694,532 169,576 17,496 132,233 27,000 489 127,082 5,168,408 Transportation and communications 3,558,659 73,437 529 39,194 8,313 — 30,858 3,710,990 Banks and other financial institutions 4,236,485 1,741 184,392 23,084 265 — 9,371 4,455,338 Government and public institutions 2,594,132 — 3,182,017 — — — — 5,776,149 Other industries (4) 2,888,378 2,996 2,148,915 8,346 375 5,447 5,434 5,059,891 Individuals 226,932 9,579,329 67,290 20,700 76,161 1,144 86,916 10,058,472 Total domestic 38,770,143 10,590,929 5,833,559 618,211 154,365 7,602 488,284 56,463,093 Foreign: Commercial and industrial 16,430,107 116 2,431,047 341,687 — 43,503 76,448 19,322,908 Banks and other financial institutions 7,988,472 — 515,716 23,389 — — 9 8,527,586 Government and public institutions 623,460 — — — — — 1,803 625,263 Other 8,271 9,024 21,527 342 65 1,170 1,300 41,699 Total foreign 25,050,310 9,140 2,968,290 365,418 65 44,673 79,560 28,517,456 Total 63,820,453 10,600,069 8,801,849 983,629 154,430 52,275 567,844 84,980,549 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) Non-impaired (4) Other industries of Domestic includes trade receivables and lease receivables of consolidated VIEs. Impaired loans 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 loans. 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. The Group classifies loans to special attention, intensive control, substantially bankrupt and bankrupt obligors as impaired loans. Impaired loans include loans past due for 90 days or more and restructured loans that meet the definition of a TDR in accordance with ASC 310, “Receivables” (“ASC 310”). There are no loans that are ninety days past due and still accruing. 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. All of the MHFG Group’s impaired loans are designated as nonaccrual loans and thus interest accruals and the amortization of net origination fees are suspended and capitalized interest is written off. Cash received on nonaccrual loans is accounted for as a reduction of the loan principal if the ultimate collectibility of the principal amount is in doubt, 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 are restored to non-impaired non-impaired Recorded investment (1) Requiring Not (2) Total Unpaid Related (3) Average Interest (4) (in millions of yen) March 31, 2018 Domestic: Manufacturing 135,083 6,987 142,070 146,857 45,750 218,899 1,869 Construction and real estate 31,557 9,276 40,833 48,752 4,411 49,926 516 Services 48,691 9,384 58,075 64,348 13,305 60,198 919 Wholesale and retail 119,463 11,421 130,884 139,556 42,798 139,333 1,842 Transportation and communications 25,019 2,508 27,527 28,480 6,862 25,672 370 Banks and other financial institutions 8,392 3,949 12,341 12,341 3,176 8,648 78 Other industries 3,650 89 3,739 3,869 3,563 4,537 53 Individuals 43,326 46,836 90,162 95,338 4,315 97,404 1,402 Total domestic 415,181 90,450 505,631 539,541 124,180 604,617 7,049 Foreign: Total foreign (5) 63,346 46,283 109,629 125,329 28,333 151,588 1,042 Total 478,527 136,733 615,260 664,870 152,513 756,205 8,091 Recorded investment (1) Requiring Not (2) Total Unpaid Related (3) Average Interest (4) (in millions of yen) September 30, 2018 Domestic: Manufacturing 111,026 6,553 117,579 122,029 40,969 129,824 714 Construction and real estate 30,818 8,837 39,655 47,362 4,032 40,244 240 Services 62,557 8,832 71,389 76,953 17,226 64,732 493 Wholesale and retail 117,212 9,870 127,082 136,833 39,610 128,983 905 Transportation and communications 28,043 2,815 30,858 31,814 8,688 29,193 198 Banks and other financial institutions 5,545 3,826 9,371 9,371 813 10,856 47 Other industries 5,357 77 5,434 5,565 4,000 4,586 15 Individuals 40,982 45,934 86,916 91,775 2,985 88,539 642 Total domestic 401,540 86,744 488,284 521,702 118,323 496,957 3,254 Foreign: Total foreign (5) 32,591 46,969 79,560 93,212 13,857 94,595 517 Total 434,131 133,713 567,844 614,914 132,180 591,552 3,771 Notes: (1) Amounts represent the outstanding balances of nonaccrual loans. The MHFG Group’s policy for placing loans in nonaccrual status 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 the allowance for groups of loans which were collectively evaluated for impairment, in addition to the allowance for those loans that were individually evaluated for impairment. The total carrying amount of the groups of loans which were collectively evaluated for impairment at March 31, 2018 and September 30, 2018 was ¥245,809 million and ¥252,407 million, respectively. (4) Amounts represent the amount of interest income on impaired loans recognized on a cash basis and included in Interest income on loans in the consolidated statements of income. (5) The majority of Total foreign consist of Commercial and Industrial loans. The remaining balance of impaired loans, which have been partially charged off, was ¥29,037 million and ¥27,759 million as of March 31, 2018 and September 30, 2018, respectively. Troubled debt restructurings The MHFG Group considers a loan modification to be a TDR when, for economic or legal reasons related to the obligor’s financial difficulties, it grants a concession to the obligor that it would not otherwise consider. The Group considers the relevant obligor to be in financial difficulty generally when its obligor rating is E2 or below. The following table presents modified loans that were determined to be TDRs during the six months ended September 30, 2017 and 2018: Loan forgiveness or debt to equity swaps Interest rate reduction Recorded investment (1) Charge-offs (in millions of yen) September 30, 2017 Domestic: Manufacturing — — 55,611 Construction and real estate — — 9,045 Services — — 18,740 Wholesale and retail — — 74,625 Transportation and communications — — 12,244 Banks and other financial institutions — — 3,461 Individuals — — 7,619 Total domestic — — 181,345 Foreign: Total foreign (2) — — 13,303 Total — — 194,648 September 30, 2018 Domestic: Manufacturing — — 51,161 Construction and real estate — — 7,764 Services — — 29,203 Wholesale and retail — — 75,593 Transportation and communications — — 13,999 Banks and other financial institutions — — 7,160 Individuals — — 8,866 Total domestic — — 193,746 Foreign: Total foreign (2) 1,008 2,012 9,493 Total 1,008 2,012 203,239 Notes: (1) Amounts represent the book values of loans immediately after the restructurings. (2) The majority of Total foreign consist of Commercial and Industrial loans. 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 six months ended September 30, 2017 and 2018 with respect to the loans modified as TDRs within the previous twelve months: Recorded investment September 30, 2017 September 30, 2018 (in millions of yen) Domestic: Manufacturing 2,006 383 Construction and real estate 70 390 Services 2,561 714 Wholesale and retail 13,396 6,700 Transportation and communications 201 409 Other industries 130 — Individuals 904 2,241 Total domestic 19,268 10,837 Foreign: Total foreign 4,588 — Total 23,856 10,837 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, 2018 and September 30, 2018: 30-59 days 60-89 days 90 days or Total past Current Total (in millions of yen) March 31, 2018 Domestic: Manufacturing 585 470 8,037 9,092 8,147,249 8,156,341 Construction and real estate 1,641 474 28,633 30,748 8,070,920 8,101,668 Services 1,977 1,142 5,051 8,170 5,015,848 5,024,018 Wholesale and retail 1,704 1,083 6,639 9,426 5,103,247 5,112,673 Transportation and communications 356 639 1,828 2,823 3,562,046 3,564,869 Banks and other financial institutions — 1,301 — 1,301 4,470,122 4,471,423 Government and public institutions — — — — 8,882,125 8,882,125 Other industries 33 12 37 82 5,018,305 5,018,387 Individuals 31,566 12,426 31,444 75,436 10,253,574 10,329,010 Total domestic 37,862 17,547 81,669 137,078 58,523,436 58,660,514 Foreign: Total foreign (Note) 897 450 41,316 42,663 24,958,163 25,000,826 Total 38,759 17,997 122,985 179,741 83,481,599 83,661,340 September 30, 2018 Domestic: Manufacturing 594 416 7,714 8,724 8,460,716 8,469,440 Construction and real estate 1,461 927 26,369 28,757 8,447,077 8,475,834 Services 1,006 1,014 4,121 6,141 5,282,430 5,288,571 Wholesale and retail 2,829 833 6,626 10,288 5,158,120 5,168,408 Transportation and communications 53 707 1,563 2,323 3,708,667 3,710,990 Banks and other financial institutions 90 6 — 96 4,455,242 4,455,338 Government and public institutions — — — — 5,776,149 5,776,149 Other industries — — 45 45 5,059,846 5,059,891 Individuals 29,699 12,522 31,885 74,106 9,984,366 10,058,472 Total domestic 35,732 16,425 78,323 130,480 56,332,613 56,463,093 Foreign: Total foreign (Note) 876 348 40,843 42,067 28,475,389 28,517,456 Total 36,608 16,773 119,166 172,547 84,808,002 84,980,549 Note: The majority of Total foreign consist of Commercial and Industrial loans. Loans held for sale Loans that have been identified for sale are classified as loans held for sale within Other assets and are accounted for at the lower of cost or fair value. The outstanding balance of loans held for sale was ¥86,153 million and ¥15,758 million at March 31, 2018 and September 30, 2018, respectively.

Allowance for loan losses

Allowance for loan losses	6 Months Ended
	Sep. 30, 2018
Allowance for loan losses	5. Allowance for loan losses The MHFG Group maintains an appropriate allowance for loan losses to absorb probable losses inherent in the loan portfolio and makes adjustments to such allowance through 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 obligor should be classified as substantially bankrupt or bankrupt. See Note 4 “Loans” for the definitions of obligor categories. Obligors 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 in the corporate and other portfolio segments, the Group separately monitors the credit quality of each obligor without using time-based triggers. Subsequent recoveries of previously charged-off 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, or (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. In obtaining the collateral, the Group evaluates the fair value of the collateral and its legal enforceability. The Group also performs subsequent re-evaluations At 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. MHFG Group’s accounting policies and the methodology used to estimate the allowance for loan losses for the other portfolio segment are equivalent to the policies and methodology used for the corporate portfolio segment. For the corporate portfolio segment, 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. For the retail portfolio segment, the different categories of past due status of loans are primarily utilized in the credit quality review and the credit rating processes as the basis for determining the allowance for loan losses. The formula allowance is applied to groups of loans that are collectively evaluated for impairment. The evaluation of the 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 therefore 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) by using the most recently available data from April 2008 for the corporate portfolio segment, and the most recently available data for the past six years for the retail portfolio segment, in the case of normal obligors; and (b) by using the most recently available data from April 2002 for the corporate and retail portfolio segments, in the case of watch obligors; and (2) the loss given default by using the most recently available data for the past six years for the corporate and retail portfolio segments. 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 defaults, if any, are considered in determining obligor categories. 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 by portfolio segments, and recent loss experience in particular segments of the portfolio. When determining the length of the period to calculate the probability of default, the Group considers the uncertainty in the economic and business conditions. 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. Changes in Allowance for loan losses by portfolio segment for the six months ended September 30, 2017 and 2018 are shown below: Corporate Retail Other Total (in millions of yen) Six months ended September 30, 2017 Balance at beginning of period 407,327 36,923 35,423 479,673 Provision (credit) for loan losses (109,379 ) (6,469 ) (2,114 ) (117,962 ) Charge-offs (17,366 ) (745 ) (3,107 ) (21,218 ) Recoveries 6,447 315 1,247 8,009 Net charge-offs (10,919 ) (430 ) (1,860 ) (13,209 ) Others (Note) 2,552 — (585 ) 1,967 Balance at end of period 289,581 30,024 30,864 350,469 Six months ended September 30, 2018 Balance at beginning of period 249,072 28,192 32,638 309,902 Provision (credit) for loan losses (13,435 ) (2,290 ) 2,445 (13,280 ) Charge-offs (27,419 ) (1,243 ) (2,602 ) (31,264 ) Recoveries 4,914 220 2,409 7,543 Net charge-offs (22,505 ) (1,023 ) (193 ) (23,721 ) Others (Note) 2,519 — (931 ) 1,588 Balance at end of period 215,651 24,879 33,959 274,489 Note: Others includes primarily foreign exchange translation. The table below presents Allowance for loan losses and loans outstanding by portfolio segment disaggregated on the basis of impairment method at March 31, 2018 and September 30, 2018: Corporate Retail Other Total (in millions of yen) March 31, 2018 Allowance for loan losses 249,072 28,192 32,638 309,902 of which individually evaluated for impairment 129,789 2,602 7,383 139,774 of which collectively evaluated for impairment 119,283 25,590 25,255 170,128 Loans (Note) 60,837,559 11,133,862 11,689,919 83,661,340 of which individually evaluated for impairment 593,053 21,364 61,023 675,440 of which collectively evaluated for impairment 60,244,506 11,112,498 11,628,896 82,985,900 September 30, 2018 Allowance for loan losses 215,651 24,879 33,959 274,489 of which individually evaluated for impairment 105,988 2,501 6,954 115,443 of which collectively evaluated for impairment 109,663 22,378 27,005 159,046 Loans (Note) 65,256,236 10,837,056 8,887,257 84,980,549 of which individually evaluated for impairment 474,645 21,723 45,420 541,788 of which collectively evaluated for impairment 64,781,591 10,815,333 8,841,837 84,438,761 Note: Amounts represent loan balances before deducting unearned income and deferred loan fees.

Other assets and liabilities

Other assets and liabilities	6 Months Ended
	Sep. 30, 2018
Other assets and liabilities	6. Other assets and liabilities The following table sets forth the details of other assets and liabilities at March 31, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 (in millions of yen) Other assets: Accounts receivable: Receivables from brokers, dealers and customers for securities transactions (1) 1,578,952 1,356,005 Other 368,030 364,631 Collateral pledged: Collateral pledged for derivative transactions 981,390 868,572 Margins provided for futures contracts 142,156 171,927 Other 965,137 906,646 Prepaid pension cost 874,191 859,484 Security deposits 126,001 125,739 Loans held for sale 86,153 15,758 Other 609,624 557,763 Total 5,731,634 5,226,525 Other liabilities: Accounts payable: Payables to brokers, dealers and customers for securities transactions (1) 1,410,785 1,986,580 Other 455,789 556,064 Guaranteed trust principal (2) 761,685 780,619 Collateral accepted: Collateral accepted for derivative transactions 598,524 700,758 Margins accepted for futures contracts 325,038 333,238 Unearned income (3) 130,916 132,364 Other 1,022,858 905,459 Total 4,705,595 5,395,082 Notes: (1) Receivables from brokers, dealers and customers for securities transactions included ¥372,395 million and ¥372,799 million of such receivables of consolidated VIEs at March 31, 2018 and September 30, 2018, respectively. Payables to brokers, dealers and customers for securities transactions included ¥422,060 million and ¥446,935 million of such payables of consolidated VIEs at March 31, 2018 and September 30, 2018, respectively. (2) Guaranteed trust principal is the liability of certain consolidated trust arrangements that meet the definition of a VIE for which the MHFG Group provides guarantees for the repayment of principal. See Note 15 “Variable interest entities and securitizations” for further discussion of the guaranteed principal money trusts. (3) Unearned income is primarily comprised of loan fees received from consumer loan customers when loans are made. This income is being deferred and recognized in earnings over the life of the loan.

Preferred and common stock

Preferred and common stock	6 Months Ended
	Sep. 30, 2018
Preferred and common stock	7. Preferred and common stock Preferred stock The composition of preferred stock at March 31, 2018 and September 30, 2018 is as follows: Class of stock March 31, 2018 September 30, 2018 Authorized Issued Authorized Issued (number of shares) Class XIV preferred stock 900,000,000 — 900,000,000 — Class XV preferred stock 900,000,000 — 900,000,000 — Class XVI preferred stock 1,500,000,000 — 1,500,000,000 — Common stock The following table shows the changes in the number of issued shares of common stock during the fiscal year ended March 31, 2018 and the six months ended September 30, 2018: March 31, 2018 September 30, 2018 (number of shares) Balance at beginning of period 25,386,307,945 25,389,644,945 Issuance of new shares of common stock due to exercise of stock acquisition rights 3,337,000 2,854,000 Balance at end of period 25,389,644,945 25,392,498,945

Accumulated other comprehensive

Accumulated other comprehensive income	6 Months Ended
	Sep. 30, 2018
Accumulated other comprehensive income	8. Accumulated other comprehensive income Changes in each component of AOCI for the six months ended September 30, 2017 and 2018 are as follows: Six months ended September 30, 2017 2018 (in millions of yen) AOCI, balance at beginning of period, previously reported 1,521,163 1,741,894 Cumulative effect of change in accounting principles (Note 2) — (1,535,142 ) AOCI, balance at beginning of period, adjusted 1,521,163 206,752 Net unrealized gains (losses) on available-for-sale Balance at beginning of period, previously reported 1,461,302 1,556,585 Cumulative effect of change in accounting principles (Note 2) — (1,525,064 ) Balance at beginning of period, adjusted 1,461,302 31,521 Unrealized holding gains (losses) during period 247,493 (25,155 ) Less: reclassification adjustments for losses (gains) included in net income (78,659 ) (862 ) Change during period 168,834 (26,017 ) Balance at end of period 1,630,136 5,504 Foreign currency translation adjustments: Balance at beginning of period (5,535 ) (35,076 ) Foreign currency translation adjustments during period (4,322 ) 7,678 Less: reclassification adjustments for losses (gains) included in net income — — Change during period (4,322 ) 7,678 Balance at end of period (9,857 ) (27,398 ) Pension liability adjustments: Balance at beginning of period 65,396 220,385 Unrealized gains (losses) during period 32 (218 ) Less: reclassification adjustments for losses (gains) included in net income 140 (2,916 ) Change during period 172 (3,134 ) Balance at end of period 65,568 217,251 Own credit risk adjustments (Note) Balance at beginning of period, previously reported — — Cumulative effect of change in accounting principles (Note 2) — (10,078 ) Balance at beginning of period, adjusted — (10,078 ) Unrealized gains (losses) during period — 2,656 Less: reclassification adjustments for losses (gains) included in net income — (20 ) Change during period — 2,636 Balance at end of period — (7,442 ) Total other comprehensive income (loss), net of tax attributable to MHFG shareholders 164,684 (18,837 ) AOCI, balance at end of period 1,685,847 187,915 Note: The MHFG Group adopted ASU No.2016-01 on April 1, 2018. The ASU requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. See Note 2 “Recently issued accounting pronouncements” for further details. The following table shows the amounts reclassified out of AOCI into net income during the six months ended September 30, 2018: Six months ended September 30, 2018 Before tax (1) Tax effect (2) Net of tax before Net of tax attributable to (2) Net of tax attributable to shareholders (in millions of yen) Amounts reclassified out of AOCI into net income: Affected line items in the consolidated statements of income: Net unrealized gains (losses) on available-for-sale 1,245 (383 ) 862 — 862 Investment gains (losses)—net Pension liability adjustments 4,102 (1,184 ) 2,918 (2 ) 2,916 Salaries and employee benefits Own credit risk adjustments 29 (9 ) 20 — 20 Other noninterest income (expenses) Total 5,376 (1,576 ) 3,800 (2 ) 3,798 Notes: (1) The amounts in the Before tax column are recorded in each account presented under the heading “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 (loss) attributable to noncontrolling interests in the consolidated statements of income, respectively.

Regulatory matters

Regulatory matters	6 Months Ended
	Sep. 30, 2018
Regulatory matters	9. 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. Capital adequacy ratios of MHFG, MHBK, and MHTB as of March 31, 2018 and September 30, 2018 calculated in accordance with Japanese GAAP and the guidelines established by the Financial Services Agency are set forth in the following table: March 31, 2018 September 30, 2018 Amount Ratio Amount Ratio (in billions of yen, except percentages) Consolidated: MHFG: Common Equity Tier 1 capital: Required (Note) 4,247 7.135 4,304 7.145 Actual 7,437 12.49 7,607 12.62 Tier 1 capital: Required (Note) 5,140 8.635 5,208 8.645 Actual 9,192 15.44 9,435 15.66 Total risk-based capital: Required (Note) 6,331 10.635 6,413 10.645 Actual 10,860 18.24 11,214 18.61 MHBK: Common Equity Tier 1 capital: Required 2,400 4.50 2,470 4.50 Actual 6,584 12.34 6,817 12.41 Tier 1 capital: Required 3,200 6.00 3,294 6.00 Actual 8,330 15.61 8,638 15.73 Total risk-based capital: Required 4,267 8.00 4,391 8.00 Actual 9,881 18.52 10,331 18.82 MHTB: Common Equity Tier 1 capital: Required 112 4.50 111 4.50 Actual 498 19.99 522 21.25 Tier 1 capital: Required 149 6.00 147 6.00 Actual 499 20.05 523 21.27 Total risk-based capital: Required 199 8.00 196 8.00 Actual 505 20.28 527 21.46 Non-consolidated: MHBK: Common Equity Tier 1 capital: Required 2,312 4.50 2,374 4.50 Actual 6,330 12.32 6,495 12.31 Tier 1 capital: Required 3,082 6.00 3,165 6.00 Actual 8,081 15.73 8,322 15.77 Total risk-based capital: Required 4,109 8.00 4,220 8.00 Actual 9,619 18.72 10,007 18.97 MHTB: Common Equity Tier 1 capital: Required 112 4.50 110 4.50 Actual 504 20.28 520 21.26 Tier 1 capital: Required 149 6.00 147 6.00 Actual 504 20.28 520 21.26 Total risk-based capital: Required 199 8.00 196 8.00 Actual 509 20.50 524 21.45 Note: The required ratios disclosed above, at March 31, 2018 and September 30, 2018, include the transitional capital conservation buffer of 1.875%, the countercyclical capital buffer of 0.01% and 0.02%, respectively, and the transitional additional loss absorbency requirements for global systemically important banks (“G-SIBs”) (“D-SIBs”) MHFG’s securities subsidiaries in Japan are also subject to the capital adequacy requirement under the Financial Instruments and Exchange Act. Failure to maintain a minimum capital ratio will trigger mandatory regulatory actions. Management believes, as of September 30, 2018, that MHFG, MHBK, MHTB, and their securities subsidiaries in Japan were in compliance with all capital adequacy requirements to which they were subject.

Earnings per common share

Earnings per common share	6 Months Ended
	Sep. 30, 2018
Earnings per common share	10. 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 period. Diluted earnings per common share reflect all dilutive potential common shares such as stock options. The following table sets forth the computation of basic and diluted earnings per common share for the six months ended September 30, 2017 and 2018: Six months ended September 30, 2017 2018 (in millions of yen) Net income: Net income attributable to MHFG common shareholders 372,549 285,270 Effect of dilutive securities — — Net income attributable to common shareholders after assumed conversions 372,549 285,270 Six months ended September 30, 2017 2018 (thousands of shares) Shares: Weighted average common shares outstanding 25,366,347 25,363,167 Effect of dilutive securities: Stock options 7,933 4,790 Weighted average common shares after assumed conversions 25,374,280 25,367,957 Six months ended September 30, 2017 2018 (in yen) Amounts per common share: Basic net income per common share 14.69 11.25 Diluted net income per common share 14.68 11.25

Income taxes

Income taxes	6 Months Ended
	Sep. 30, 2018
Income taxes	11. Income taxes The following table presents the components of Income tax expense for the six months ended September 30, 2017 and 2018: Six months ended September 30, 2017 2018 (in millions of yen) Current tax expense 99,238 114,666 Deferred tax expense (benefit) 20,095 (28,961 ) Total income tax expense 119,333 85,705 The preceding table does not reflect the tax effects of items recorded directly in Equity for the six months ended September 30, 2017 and 2018. The detailed amounts recorded directly in Equity are as follows: Six months ended September 30, 2017 2018 (in millions of yen) Net unrealized gains (losses) on available-for-sale Unrealized gains (losses) 105,819 (11,292 ) Less: reclassification adjustments (35,053 ) (383 ) Total 70,766 (11,675 ) Pension liability adjustments: Unrealized gains (losses) 11 (97 ) Less: reclassification adjustments 96 (1,184 ) Total 107 (1,281 ) Own credit risk adjustments (Note) Unrealized gains (losses) — 967 Less: reclassification adjustments — (9 ) Total — 958 Total tax effect before allocation to noncontrolling interests 70,873 (11,998 ) Note: The MHFG Group adopted ASU No.2016-01 on April 1, 2018. The ASU requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. See Note 2 “Recently issued accounting pronouncements” for further details. The statutory tax rates were 30.86% and 30.62% as of September 30, 2017 and 2018, respectively. The effective tax rates, 23.27% and 20.52% for the six months ended September 30, 2017 and 2018, respectively, differed from the statutory tax rates. The difference of the tax rates for the six months ended September 30, 2017 consisted of number of tax beneficial items including a decrease in valuation allowance related to the MHFG’s foreign subsidiaries in the United States and a change in deferred tax liabilities related to undistributed earnings of certain domestic subsidiaries. The difference of the tax rates for the six months ended September 30, 2018 consisted of number of tax beneficial items including a decrease in deferred tax liabilities related to undistributed earnings of certain foreign subsidiaries. At September 30, 2018, the MHFG Group had net operating loss carryforwards totaling ¥720 billion. The total amount of unrecognized tax benefits was ¥2,965 million at September 30, 2018, 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. A portion of unrecognized tax benefits at March 31, 2018 was resolved in the six months period ended September 30, 2018, of which the amount was immaterial. The amount of additional unrecognized tax benefits for the period related to the tax positions taken was also immaterial. 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 bene

Pension and other employee benefit plans	6 Months Ended
	Sep. 30, 2018
Pension and other employee benefit plans	12. Pension and other employee benefit plans The following table summarizes the components of net periodic benefit cost of the severance indemnities and pension plans of the MHFG Group for the six months ended September 30, 2017 and 2018: Six months ended September 30, 2017 2018 (in millions of yen) Service cost-benefits earned during the period 21,643 21,726 Interest costs on projected benefit obligations 3,609 3,331 Expected return on plan assets (17,353 ) (19,124 ) Amortization of prior service benefits 102 76 Amortization of net actuarial loss (gain) 214 (3,942 ) Special termination benefits 2,128 1,792 Net periodic benefit cost 10,343 3,859 As previously disclosed in the consolidated financial statements for the fiscal year ended March 31, 2018, the total contribution of approximately ¥52 billion is expected to be paid to the pension plans during the fiscal year ending March 31, 2019. For the six months ended September 30, 2018, the total contribution of ¥26 billion has been paid to the pension plans. The additional contribution of ¥26 billion is expected to be paid during the remainder of the fiscal year ending March 31, 2019 for a total of ¥52 billion.

Derivative financial instrument

Derivative financial instruments	6 Months Ended
	Sep. 30, 2018
Derivative financial instruments	13. Derivative financial instruments The MHFG Group enters 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. Counterparty 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 counterparty 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 counterparty 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 and fair value amounts of derivative instruments The following table summarizes the notional and fair value amounts of derivative instruments outstanding as of March 31, 2018 and September 30, 2018. The fair values of derivatives are presented on a gross basis, derivative receivables and payables are not offset. In addition, they are not offset against the amounts recognized for 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) March 31, 2018 Notional amount (1) Designated Not designated Designated Not designated (in billions of yen) Interest rate contracts 1,004,169 — 7,176 — 7,143 Foreign exchange contracts 155,832 2 2,695 — 2,382 Equity-related contracts 6,189 — 197 9 142 Credit-related contracts 2,708 — 18 — 21 Other contracts 335 — 23 — 19 Total 1,169,233 2 10,109 9 9,707 Fair value Derivative receivables (2) Derivative payables (2) September 30, 2018 Notional amount (1) Designated Not designated Designated Not designated (in billions of yen) Interest rate contracts 1,057,838 — 4,607 — 4,520 Foreign exchange contracts 152,512 — 2,367 — 2,134 Equity-related contracts 6,201 — 315 — 214 Credit-related contracts 2,909 — 22 — 22 Other contracts 356 — 49 — 46 Total 1,219,816 — 7,360 — 6,936 Notes: (1) Notional amount includes 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, which was not offset against derivative positions, was included in Other assets and Other liabilities, respectively, of which the amounts were ¥981 billion and ¥599 billion at March 31, 2018, and ¥869 billion and ¥701 billion at September 30, 2018, 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 forward contracts to modify exposure to changes in the fair value of Equity securities. The Group adopted ASU No.2016-01 Before the adoption of the ASU, 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 were 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 was recorded in Trading account gains (losses)—net. No ineffectiveness existed because the MHFG Group chose to exclude changes in the differences between the spot and the forward prices from the effectiveness test. If the hedge relationship was terminated, the fair value adjustment to the hedged item continued to be reported as part of the basis of the item. The fair value adjustment was recognized in earnings upon the sale of the hedged item. The following table summarizes gains and losses information related to fair value hedges for the six months ended September 30, 2017: Gains (losses) recorded in income Six months ended September 30, 2017 Derivatives Hedged Hedge Net gain (loss) excluded (in millions of yen) Equity-related contracts (22,493 ) 20,208 — (2,285 ) Total (22,493 ) 20,208 — (2,285 ) 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 The following table summarizes gains and losses information related to net investment hedges for the six months ended September 30, 2017 and 2018: Gains (losses) recorded in income and other comprehensive income (“OCI”) 2017 2018 Effective portion Ineffective portion Effective portion Ineffective portion (in millions of yen) Financial instruments hedging foreign exchange risk 3,487 196 1,937 (32 ) Total 3,487 196 1,937 (32 ) Note: Related to the effective portion of net investment hedges, gains of ¥186 million were reclassified from Accumulated other comprehensive income to earnings for the six months ended September 30, 2018. No amount related to the effective portion of net investment hedges was reclassified from Accumulated other comprehensive income to earnings for the six months ended September 30, 2017. 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 strategies: (1) interest-rate swap transactions for the purpose of economically managing the interest-rate risks in deposits, loans etc., (2) currency swap transactions for the purpose of economically managing the foreign exchange risk of these assets, and (3) credit derivatives for the purpose of economically managing the credit risk in loans, residential mortgage-backed securities (“RMBS”), commercial mortgage-backed securities (“CMBS”), collateralized loan obligations (“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 six months ended September 30, 2017 and 2018: Gains (losses) recorded in income 2017 2018 (in millions of yen) Interest rate contracts 26,648 (75,324 ) Foreign exchange contracts (4,511 ) 26,706 Equity-related contracts (1) (41,869 ) 20,432 Credit-related contracts (2) (3,371 ) (35 ) Other contracts 494 (785 ) Total (22,609 ) (29,006 ) 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 gain (loss) of ¥(273) million and ¥(215) million on the credit derivatives economically managing the credit risk of loans during the six months ended September 30, 2017 and 2018, 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 the 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, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 Notional amount Fair value Notional amount Fair value (in billions of yen) Credit protection written: Investment grade 1,105 15 1,182 14 Non-investment 197 4 252 5 Total 1,302 19 1,434 19 Credit protection purchased 1,541 (22 ) 1,627 (19 ) 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 - non-investment Non-investment The following table shows the maximum potential amount of future payments for credit protection written by expiration period at March 31, 2018 and September 30, 2018: Maximum payout/Notional amount March 31, 2018 September 30, 2018 (in billions of yen) One year or less 329 322 After one year through five years 831 927 After five years 142 185 Total 1,302 1,434 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 effect of any amounts that the Group may possibly collect on 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 following table shows the quantitative information about derivative instruments with credit-risk-related contingent features at March 31, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 (in billions of yen) Aggregate fair value of derivative instruments with credit-risk-related contingent features in net liability positions 572 548 Collateral provided to counterparties in the normal course of business 593 514 Amount required to be posted as collateral or settled immediately if credit-risk-related contingent features were triggered (Note) — 34 Note: There was no amount that the Group would be required to post as collateral or settle immediately on March 31, 2018.

Commitments and contingencies

Commitments and contingencies	6 Months Ended
	Sep. 30, 2018
Commitments and contingencies	14. 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 Group records all guarantees and similar obligations subject to ASC 460, “Guarantees” (“ASC 460”) at fair value in the consolidated balance sheets at the inception of the guarantee. The table below summarizes the maximum potential amount of future payments by type of guarantee at March 31, 2018 and September 30, 2018. The maximum potential amount of future payments disclosed below represents the contractual amounts that could be required to 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. March 31, September 30, (in billions of yen) Performance guarantees 2,165 2,205 Guarantees on loans 241 393 Guarantees on securities 164 173 Other guarantees 2,210 2,076 Guarantees for the repayment of trust principal 709 754 Liabilities of trust accounts 13,861 12,172 Derivative financial instruments 11,654 12,941 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, 2018 and September 30, 2018: March 31, September 30, (in billions of yen) Investment grade 3,930 3,964 Non-investment 850 883 Total 4,780 4,847 Note: Investment grade in the internal rating scale generally corresponds to BBB- or above in the external rating scale. Other off-balance-sheet In addition to guarantees, the MHFG Group issues other off-balance-sheet The table below summarizes the contractual amounts with regard to these undrawn commitments at March 31, 2018 and September 30, 2018: March 31, September 30, (in billions of yen) Commitments to extend credit (Note) 78,448 82,194 Commercial letters of credit 690 817 Total 79,138 83,011 Note: Commitments to extend credit include commitments to invest in securities. 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 the 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 in respect of the collateral and the subsidiary 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 and 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.

Variable interest entities and

Variable interest entities and securitizations	6 Months Ended
	Sep. 30, 2018
Variable interest entities and securitizations	15. 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, structured finance, and funding vehicles. 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 the 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 has determined 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 possibly be required to record in its consolidated statements of income as a result of its involvement with the VIEs. This represents exposures associated with both on-balance-sheet off-balance-sheet The table below shows the 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, 2018 and September 30, 2018: Consolidated VIEs Significant March 31, 2018 Consolidated assets Total assets Maximum (in billions of yen) Asset-backed commercial paper/loan programs 2,185 — — Asset-backed securitizations 627 78 5 Investments in securitization products 374 — — Investment funds 2,661 1,891 533 Trust arrangements and other 21 — — Total 5,868 1,969 538 Consolidated VIEs Significant September 30, 2018 Consolidated assets Total assets Maximum (in billions of yen) Asset-backed commercial paper/loan programs 2,082 — — Asset-backed securitizations 573 78 9 Investments in securitization products 373 — — Investment funds 2,913 1,374 436 Trust arrangements and other 21 — — Total 5,962 1,452 445 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 significant unconsolidated VIEs, as of March 31, 2018 and September 30, 2018: Assets on balance sheets related to unconsolidated VIEs: March 31, 2018 September 30, 2018 (in billions of yen) Trading account assets 89 95 Investments 210 136 Loans 163 133 Total 462 364 Liabilities on balance sheets and maximum exposure to loss related to unconsolidated VIEs: March 31, 2018 September 30, 2018 (in billions of yen) Payables under securities lending transactions 38 42 Trading account liabilities 1 1 Total 39 43 Maximum exposure to loss (Note) 538 445 Note: This represents the maximum amount the Group could possibly be required to record in its consolidated statements of income associated with on-balance-sheet off-balance-sheet Asset-backed commercial paper/loan programs The MHFG Group manages several asset-backed commercial paper/loan programs that provide its clients with off-balance-sheet Asset-backed securitizations The MHFG Group acts as an arranger of various types of structured finance to meet its clients’ needs for off-balance-sheet 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 in 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 by 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 and holds retained subordinated beneficial interests in the securitized mortgage loans. In addition, the Group retains credit exposure in the form of guarantees on these 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 its retained interests and its aforementioned involvement as a guarantor, 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 amounts of the securities and the loans are generally limited to the amounts invested because the Group has no contractual involvement in such VIEs beyond its investments. Since the Group is involved in these 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 are to be held by 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 the 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 about such investment funds. The Group determines whether it is the primary beneficiary by evaluating whether it has both (1) the power to make investment decisions about the investment funds and (2) the obligation to absorb losses or the right to receive benefits that could potentially be significant to the investment funds. The Group consolidates certain investment funds where it is deemed to be the primary beneficiary. 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 by the VIEs or to manage these assets. In addition, through the principal guarantee agreements, the Group has the obligation to absorb losses that could potentially be significant to the VIEs. Therefore, the Group consolidates such 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. See Note 14 “Commitments and contingencies” for the balances of guaranteed trust principal that are not consolidated at March 31, 2018 and September 30, 2018. With respect to non-guaranteed non-guaranteed 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 may sometimes act as an interest rate swap counterparty, the Group has determined that it does not have the power to direct the activities of the VIEs that most significantly impact the VIEs’ economic performance, or it does not have significant variable interests. Funding Vehicles The MHFG Group has established several wholly-owned off-shore Securitization The MHFG Group engages in securitization activities and securitizes mortgage loans, other loans, government and corporate securities and other types of financial assets in the normal course of business. In these securitization transactions, the Group records the transfer of a financial asset as a sale when all the accounting criteria for a sale under ASC 860, “Transfers and Servicing” (“ASC860”) are met. These criteria are (1) the transferred financial assets are legally isolated from the Group’s creditors, (2) the transferee or beneficial interest holder has the right to pledge or exchange the transferred financial assets, and (3) the Group does not maintain effective control over the transferred financial assets. If all the criteria are not met, the transfer is accounted for as a secured borrowing. For the six months ended September 30, 2017 and 2018, the MHFG Group neither made significant transfers of financial assets nor recognized significant gains or losses in securitization transactions accounted for as sales. The Group did not retain significant interests in securitization transactions accounted for as sales as of March 31, 2018 and September 30, 2018. There are certain transactions where transfers of financial assets do not qualify for the aforementioned sales criteria and 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 ¥208 billion and ¥89 billion as of March 31, 2018, and ¥198 billion and ¥101 billion as of September 30, 2018, 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.

Noninterest income

Noninterest income	6 Months Ended
	Sep. 30, 2018
Noninterest income	16. Noninterest income Details of Noninterest income for the six months ended September 30, 2017 and 2018 are as follows: Six months ended September 30, 2017 2018 (in millions of yen) Fee and commission income: Securities-related business (1) 85,897 79,138 Deposits and lending business (2) 65,081 70,647 Remittance business (1) 54,166 55,078 Asset management business (1) 50,322 49,818 Trust related business (1) 54,367 57,372 Agency business (1) 18,261 19,509 Guarantee related business (3) 13,899 14,234 Fees for other customer services (1) 59,238 67,931 Total Fee and commission income 401,231 413,727 Foreign exchange gains (losses)—net (3) 50,765 44,718 Trading account gains (losses)—net (2) 235,339 64,956 Investment gains (losses)—net: Debt securities (3) 16,099 2,485 Equity securities (3) 109,390 306,788 Equity in earnings (losses) of equity method investees—net (3) 10,389 22,627 Gains on disposal of premises and equipment (3) 4,567 4,305 Other noninterest income (2) 33,158 48,950 Total 860,938 908,556 Notes: (1) These amounts are revenues from contracts within the scope of ASC 606, “Revenue from contracts with customers” (“ASC 606”). (2) Part of these amounts are considered to be revenues from contracts that are within the scope of ASC 606. (3) These amounts are revenues from contracts that do not meet the scope of ASC 606. Certain Fee and commission income, Trading account gains (losses)—net and Other noninterest income outlined in the table above are considered to be revenues from contracts that are within the scope of ASC 606. The MHFG Group disaggregates Fee and commission income, which is the main part of revenues within the scope of ASC 606, by type of business or service in the table above. Fee and commission income Securities-related business fees mainly consist of brokerage fees and commissions, and asset-based revenues. Brokerage fees and commissions mainly include fees earned from the execution of customer transactions and sales commissions of investment trusts. Brokerage fees and commissions are recognized at the point in time on transaction date. Asset-based revenues mainly include fees received from investment trust management companies in return for administration services, such as record keeping services, of investment trusts. The amounts of asset-based revenues are calculated based on customer’s net asset value and recognized over time in the period when the related service is provided. Deposits and lending business fees consist of deposit-related fees and lending-related fees. Most of the deposit-related fees are within the scope of ASC 606, while most of the lending-related fees such as commitment fees and arrangement fees are not. Deposit-related fees within the scope of ASC 606 include service charges on consumer and commercial deposit accounts such as account transfer charges. Deposit-related fees are recognized at the point in time when the transactions occur or the related service is provided. Remittance business fees include service charges for domestic and international funds transfers and collections. These fees are recognized at the point in time when the related service is provided. Asset management business fees consist of investment trust management fees and investment advisory fees for investment trusts. These fees are received from investment trusts in return for asset management services and/or investment advisory services on behalf of customers. The amounts of these fees are calculated based on a percentage of customer’s net asset value. These fees are recognized over time in the period when the management and/or advisory service is provided and the amount is fixed. Trust related business fees consist of trust fees and fees related to trust business, which amounted to ¥26 billion and ¥31 billion for the six months ended September 30, 2018, respectively. Trust fees are earned primarily through fiduciary asset management and administration services for corporate pension plans and investment funds. These fees are recognized over time in the period when the related service is provided. Fees related to trust business mainly include brokerage commissions of real estate property, sales commissions of beneficial interest in real estate trust and charges for stock transfer agent services. Fees related to trust business are mainly earned on a transaction basis and recognized at the point in time when the related service is provided. Agency business fees mainly include administration service fees related to the MHFG Group’s agency business such as Japan’s principal public lottery program and revenues from standing proxy services. These fees are recognized at the point in time when the related service is provided. Fees for other customer services include various revenues such as sales commissions of life insurance, service charges for electronic banking, financial advisory fees, and service charges for software development. Sales commissions from life insurance sales are received from insurance companies in return for selling insurance products and recognized when the insurance product is sold to customers. Service charges for electronic banking are mainly monthly basic usage fees and recognized over the related transaction period. Financial advisory fees are recognized over time in the period when the related advisory service based on the contract is rendered. Service charges for software development are recognized over time according to the progress of the development. Trading account gains (losses)—net and Other noninterest income In addition to Fee and commission income, Trading account gains (losses)—net and Other noninterest income include certain revenues within the scope of ASC 606. Underwriting fees from trading securities, which amounted to ¥31 billion for the six months ended September 30, 2018, are within the scope of ASC 606 and accounted for in Trading account gains (losses)—net. Underwriting fees are recognized at the point in time when trade terms are fixed. For the six months ended September 30, 2018, approximately ¥14 billion of Other noninterest income was within the scope of ASC 606. Credit card interchange fees are within the scope of ASC 606 and accounted for in Other noninterest income. Credit card interchange fees are earned on credit card transactions conducted through payment networks and recognized upon settlement of the credit card payment transactions. Contract balances relating to revenues from contracts with customers subject to ASC 606 Contract assets and receivables from contracts with customers subject to ASC 606 are recognized in Accrued income or accounts receivable of Other assets. As of September 30, 2018, the balance of contract assets was not material. Contract liabilities are recognized in unearned income of Other liabilities. As of September 30, 2018, the balance of contract liabilities was not material. Remaining performance obligations relating to revenues from contracts with customers subject to ASC 606 Remaining performance obligations are services that the MHFG Group has committed to provide in the future in connection with its contracts with customers. As of September 30, 2018, the amount of expected revenues from current obligations to provide services in the future is not material. It excludes revenues from contracts less than one year or contracts that have provisions that allow the Group to recognize revenue at the amount it has the right to invoice.

Fair value

Fair value	6 Months Ended
	Sep. 30, 2018
Fair value	17. Fair value Fair value measurements ASC 820, “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 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 valuation policies which govern the principles of fair value measurements and the authority and duty of each department. The Group has also established 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 performed 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. Price verification performed 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 “ Available-for-sale 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 six months ended September 30, 2018, 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 equity 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 pricing models 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 securitization products such as RMBS, CMBS, ABS, and CLO 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. Hedge funds the Group invests in are primarily multi strategy funds that employ a fundamental bottom-up start-up ten-year 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 Available-for-sale The fair values of available-for-sale non-binding Equity securities Equity securities mainly consist of marketable equity securities. The fair values of the marketable equity securities are based upon quoted market prices for identical equity securities trading as securities in an active market. Equity securities also include securities measured at the NAV per share. Other investments Other investments consist of investments held by consolidated investment companies. These companies typically hold investments in marketable and non-marketable non-marketable Non-marketable Long-term debt Fair value accounting is elected for certain long-term debt instruments with embedded derivatives. The fair values are determined using a discounted cash flow model that considers the embedded derivatives and the terms and payment structures of the notes. The fair values of the derivatives embedded in such notes are primarily derived by using the same procedures described in “Derivative financial instruments” Items measured at fair value on a recurring basis Assets and liabilities measured at fair value on a recurring basis at March 31, 2018 and September 30, 2018, including those for which the MHFG Group has elected the fair value option, are summarized below: March 31, 2018 Level 1 Level 2 Level 3 Assets/ (in billions of yen) Assets: Trading securities (1) Japanese government bonds 1,375 43 — 1,418 Japanese local government bonds — 107 — 107 U.S. Treasury bonds and federal agency securities 2,442 209 — 2,651 Other foreign government bonds 1,682 480 — 2,162 Agency mortgage-backed securities — 1,799 — 1,799 Residential mortgage-backed securities — — 12 12 Certificates of deposit and commercial paper — 643 — 643 Corporate bonds and other 25 1,992 1,013 3,030 Equity securities 1,642 — 23 1,665 Trading securities measured at net asset value (2) 705 Derivative financial instruments: Interest rate contracts 39 7,089 48 7,176 Foreign exchange contracts 17 2,667 13 2,697 Equity-related contracts 82 110 5 197 Credit-related contracts — 16 2 18 Other contracts 6 8 9 23 Available-for-sale Japanese government bonds 12,435 897 — 13,332 Japanese local government bonds — 239 — 239 U.S. Treasury bonds and federal agency securities 686 — — 686 Other foreign government bonds 355 703 — 1,058 Agency mortgage-backed securities — 889 — 889 Residential mortgage-backed securities — 65 54 119 Commercial mortgage-backed securities — — 441 441 Japanese corporate bonds and other debt securities — 1,827 163 1,990 Foreign corporate bonds and other debt securities — 799 80 879 Equity securities (marketable) (3) 3,912 121 — 4,033 Other investments — — 38 38 Total assets measured at fair value on a recurring basis 24,698 20,703 1,901 48,007 Liabilities: Trading securities sold, not yet purchased 2,777 618 4 3,399 Derivative financial instruments: Interest rate contracts 42 7,074 27 7,143 Foreign exchange contracts 11 2,370 1 2,382 Equity-related contracts 81 69 1 151 Credit-related contracts — 20 1 21 Other contracts 4 6 9 19 Long-term debt (4) — 1,395 561 1,956 Total liabilities measured at fair value on a recurring basis 2,915 11,552 604 15,071 September 30, 2018 Level 1 Level 2 Level 3 Assets/ (in billions of yen) Assets: Trading securities (1) Japanese government bonds 1,935 32 — 1,967 Japanese local government bonds — 93 — 93 U.S. Treasury bonds and federal agency securities 2,664 193 — 2,857 Other foreign government bonds 1,705 492 — 2,197 Agency mortgage-backed securities — 1,865 — 1,865 Residential mortgage-backed securities — — 12 12 Certificates of deposit and commercial paper — 1,322 — 1,322 Corporate bonds and other 31 2,198 1,105 3,334 Equity securities 1,724 — 29 1,753 Trading securities measured at net asset value (2) 661 Derivative financial instruments: Interest rate contracts 40 4,530 37 4,607 Foreign exchange contracts 16 2,323 28 2,367 Equity-related contracts 77 220 18 315 Credit-related contracts — 20 2 22 Other contracts 12 8 29 49 Available-for-sale Japanese government bonds 12,444 1,007 — 13,451 Japanese local government bonds — 240 — 240 U.S. Treasury bonds and federal agency securities 1,134 — — 1,134 Other foreign government bonds 451 792 — 1,243 Agency mortgage-backed securities — 871 — 871 Residential mortgage-backed securities — 63 46 109 Commercial mortgage-backed securities — — 469 469 Japanese corporate bonds and other debt securities — 1,883 156 2,039 Foreign corporate bonds and other debt securities — 770 145 915 Equity securities (3) Equity securities with readily determinable fair values 4,413 90 — 4,503 Equity securities measured at net asset value (2) 35 Other investments — — 41 41 Total assets measured at fair value on a recurring basis 26,646 19,012 2,117 48,471 Liabilities: Trading securities sold, not yet purchased 2,538 268 2 2,808 Derivative financial instruments: Interest rate contracts 38 4,468 14 4,520 Foreign exchange contracts 16 2,115 3 2,134 Equity-related contracts 107 103 4 214 Credit-related contracts — 20 2 22 Other contracts 7 10 29 46 Long-term debt (4) — 1,768 612 2,380 Total liabilities measured at fair value on a recurring basis 2,706 8,752 666 12,124 Notes: (1) Trading securities include foreign currency denominated securities for which the MHFG Group elected the fair value option. (2) In accordance with ASC 820, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented for these classes of assets are intended to permit the reconciliation of the fair value hierarchy to the amounts presented in the statements of financial position. The amounts of unfunded commitments related to these investments at March 31, 2018 and September 30, 2018 were ¥31 billion and ¥40 billion, respectively. (3) The MHFG Group adopted ASU No.2016-01 on April 1, 2018. In connection with the adoption, equity securities are no longer classified as available-for-sale securities. See Note 2 “Recently issued accounting pronouncements” for further details. (4) Amounts represent items for which the Group elected the fair value option or for which it applied the practicability exception. 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 six months ended September 30, 2017 and 2018: Six months ended September 30, 2017 April 1, Gains Gains Transfers Transfers Purchases Sales Issuances Settle- September 30, Change in (losses) (6) (in billions of yen) Assets: Trading securities: Residential mortgage-backed securities 15 — (2) — — — — — — (1 ) 14 — Corporate bonds and other 1,052 18 (2) — 123 (240 ) 562 (276 ) — (153 ) 1,086 20 Equity securities 23 (1 ) (2) — — — — — — — 22 (1 ) Derivative financial instruments, net (1) Interest rate contracts 26 (6 ) (2) — — — — — — 1 21 (6 ) Foreign exchange contracts 8 (2 ) (2) — — — — — — — 6 (2 ) Equity-related contracts (25 ) (7 ) (2) — — — — — — 6 (26 ) (8 ) Other contracts — — (2) — — — — — — 1 1 — Available-for-sale Residential mortgage-backed securities 77 — (3) — (4) — — 1 — — (10 ) 68 — Commercial mortgage-backed securities 224 — (3) — (4) — — 40 (7 ) — — 257 — Japanese corporate bonds and other debt securities 174 (1 ) (3) (3 ) (4) — — 11 — — (16 ) 165 (1 ) Foreign corporate bonds and other debt securities 110 — (3) 1 (4) 15 (29 ) — — — — 97 — Other investments 37 — (3) — — — 12 — — (10 ) 39 — Liabilities: Trading securities sold, not yet purchased — — (2) — — — (57 ) 61 — — 4 — Long-term debt 593 (13 ) (5) — 1 (10 ) — — 47 (81 ) 563 (14 ) Six months ended September 30, 2018 April 1, Gains Gains Transfers Transfers Purchases Sales Issuances Settle- September 30, Change in (losses) (6) (in billions of yen) Assets: Trading securities: Residential mortgage-backed securities 12 — (2) — — — — — — — 12 — Corporate bonds and other 1,013 31 (2) — — — 457 (242 ) — (154 ) 1,105 35 Equity securities 23 2 (2) — — — 5 (1 ) — — 29 — Derivative financial instruments, net (1) Interest rate contracts 21 1 (2) — — — — — — 1 23 2 Foreign exchange contracts 12 15 (2) — — — — — — (2 ) 25 17 Equity-related contracts 4 (4 ) (2) — — — — — — 14 14 — Credit-related contracts 1 (3 ) (2) — — — — — — 2 — — Available-for-sale Residential mortgage-backed securities 54 — (3) — (4) — — — — — (8 ) 46 — Commercial mortgage-backed securities 441 — (3) — (4) — — 57 (28 ) — (1 ) 469 — Japanese corporate bonds and other debt securities 163 10 (3) (8 ) (4) — — 7 (7 ) — (9 ) 156 10 Foreign corporate bonds and other debt securities 80 — (3) — (4) 61 — 4 — — — 145 — Other investments 38 1 (3) — — — 13 — — (11 ) 41 2 Liabilities: Trading securities sold, not yet purchased 4 1 (2) — — — (30 ) 29 — — 2 — Long-term debt 561 2 (5) 3 (4) 2 — — — 85 (31 ) 612 4 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 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 were attributable to the change in fair value relating to assets and liabilities classified as Level 3 that were still held at September 30, 2017 and 2018. 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 six months ended September 30, 2017, the transfers into Level 3 included ¥123 billion of Trading securities, ¥15 billion of Available-for-sale Available-for-sale Available-for-sale Available-for-sale During the six months ended September 30, 2018, the transfers into Level 3 included ¥61 billion of Available-for-sale Available-for-sale 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, 2018 and September 30, 2018: March 31, 2018 Products/Instruments Fair value Principal valuation technique Unobservable inputs Range of input values Weighted average (5) (in billions of yen, except for percentages and basis points) Trading securities and Available-for-sale Residential mortgage-backed securities 66 Discounted cash flow Price-based Prepayment rate Default rate Recovery rate Discount margin 3% - 17% 0% - 1% 100% - 100% 17bps - 170bps 7% Commercial mortgage-backed securities 441 Discounted cash flow Price-based Discount margin 9bps - 141bps 28bps Corporate bonds and other debt securities 1,256 Discounted cash flow Price-based Prepayment rate (1) Default rate (1) Recovery rate (1) Discount margin (1) Discount margin (2) 26% - 37% 1% - 2% 60% - 69% 12bps - 1,165bps 36% Derivative financial instruments, net: Interest rate contracts 21 Internal valuation model (3) IR – IR correlation Default rate (4) 23% - 100% 0% - 63% Foreign exchange contracts 12 Internal valuation model (3) FX – IR correlation FX – FX correlation Default rate (4) 16% - 53% 61% - 61% 0% - 63% Equity-related contracts 4 Internal valuation model (3) Equity – IR correlation Equity volatility 25% - 25% 12% - 41% Credit-related contracts 1 Internal valuation model (3) Default rate Credit correlation 0% - 3% 27% - 100% Long-term debt 561 Internal valuation model (3) IR – IR correlation FX – IR correlation FX – FX correlation Equity – IR correlation Equity – FX correlation Equity correlation Equity volatility Default rate Credit correlation 23% - 100% 9% - 53% 61% - 61% 25% - 25% 55% - 70% 24% - 100% 0% - 2% 28% - 100% September 30, 2018 Products/Instruments Fair value Principal valuation technique Unobservable inputs Range of input values Weighted average (5) (in billions of yen, except for percentages and basis points) Trading securities and Available-for-sale Residential mortgage-backed securities 58 Discounted cash flow Price-based Prepayment rate Default rate Recovery rate Discount margin 4% - 18% 0% - 1% 100% - 100% 15bps - 170bps 7% Commercial mortgage-backed securities 469 Discounted cash flow Price-based Discount margin 9bps - 198bps 24bps Corporate bonds and other debt securities 1,406 Discounted cash flow Price-based Prepayment rate (1) Default rate (1) Recovery rate (1) Discount margin (1) Discount margin (2) 27% - 27% 2% - 2% 69% - 69% 93bps - 1,194bps 27% Derivative financial instruments, net: Interest rate contracts 23 Internal valuation model (3) IR – IR correlation Default rate (4) 23% - 100% Foreign exchange contracts 25 Internal valuation model (3) FX – IR correlation FX – FX correlation Default rate (4) 5% - 55% 64% - 64% 0% - 63% Equity-related contracts 14 Internal valuation model (3) Equity – IR correlation Equity correlation Equity volatility 25% - 25% Credit-related contracts — Internal valuation model (3) Default rate Credit correlation 0% - 4% 28% - 100% Long-term debt 612 Internal valuation model (3) IR – IR correlation FX – IR correlation FX – FX correlation Equity – IR correlation Equity – FX correlation Equity correlation Equity volatility Default rate Credit correlation 23% - 100% 64% - 64% 0% - 4% 24% - 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 analyses. (5) Weighted averages are calculated by weighting each input by the relative fair value of the respective financial instruments. IR = Interest rate FX = Foreign exchange Sensitivities to unobservable inputs and interrelationships 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. 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, 2018 and September 30, 2018: March 31, 2018 Total Level 1 Level 2 Level 3 Aggregate cost (in billions of yen) Assets: Loans 113 — — 113 164 Loans held-for-sale 60 — 60 — 74 Equity securities (without readily determinable fair values) 1 — — 1 3 Premises and equipment—net — — — — 4 Total assets measured at fair value on a nonrecurring basis 174 — 60 114 245 September 30, 2018 Total Level 1 Level 2 Level 3 Aggregate cost (in billions of yen) Assets: Loans 113 — — 113 162 Equity securities (without readily determinable fair values) 3 — — 3 2 Other investments 5 5 — — 7 Premises and equipment—net — — — — 2 Total assets measured at fair value on a nonrecurring basis 121 5 — 116 173 Note: The fair values may not be current as of the dates indicated, but rather as of the date the fair value change occurred. Accordingly, the carrying values may not equal current fair value. Loans in the table above have been impaired and measured based upon the fair value of the underlying collateral. Loans held-for-sale Equity securities (without readily determinable fair values) in the table above consist of non-marketable non-marketable non-marketable non-marketable Other investments in the table above includes certain equity method investments which 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. Premises and equipment–net in the table above have been impaired and written down to fair value. Fair value option The MHFG Group elected the fair value option for certain eligible financial instruments described below. Foreign currency denominated available-for-sale The MHFG Group elected the fair value option for foreign currency denominated available-for-sale available-for-sale No.2016-01. available-for-sale available-for-sale 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. In addition, the Group measures certain notes that contain embedded derivatives at fair value under the practicability exception. These notes continue to be reported in Long-term debt and interest on these 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 notes and the aggregate unpaid principal balance of such instruments were ¥21 billion and ¥33 billion at March 31, 2018 and September 30, 2018, respectively. The net unrealized gains (losses) resulting from changes in fair values of these notes recorded in Other noninterest income (expenses) were of ¥(28) billion and ¥8 billion for the six months ended September 30, 2017 and 2018, respectively. The Group records changes in fair value on these notes attributable to the instrument-specific credit risk in AOCI in accordance with ASU No.2016-01, which was adopted on April 1, 2018. Changes in fair value resulting from changes in instrument-specific credit risk were estimated by incorporating the Company’s current credit spreads observable in the bond market. Fair value of financial instruments ASC 825, “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. The following is a description of the valuation methodologies used for estimating the fair value of financial assets and liabilities not carried at fair value on the MHFG Group’s consolidated balance sheets. 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 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 available-for-sale non-marketable Loans Loans have been fair valued based on the type of loan, credit quality, prepayment assumptions and remaining maturity. The fair value of 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 collateral dependent impaired loans is determined based on the fair value of the underlying collateral. 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 in Note 6 “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 other 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 in Note 6 “Other assets and liabilities”. The fair value of certain off-balance-sheet The following table shows the carrying amounts and fair values at March 31, 2018 and September 30, 2018, of certain financial instruments, excluding financial instruments which are carried at fair value on a

Offsetting of financial assets

Offsetting of financial assets and financial liabilities	6 Months Ended
	Sep. 30, 2018
Offsetting of financial assets and financial liabilities	18. 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 table provides information about the offsetting of financial assets and financial liabilities at March 31, 2018 and September 30, 2018. The table includes 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 recognized Gross amounts offset on the balance sheet Net amounts presented on the balance sheet (2) Financial instruments (4) Cash collateral Net (in billions of yen) March 31, 2018 Assets (1) Derivatives 9,341 — 9,341 (7,751 ) (520 ) 1,070 Receivables under resale agreements 7,804 — 7,804 (7,763 ) — 41 Receivables under securities borrowing transactions 3,904 — 3,904 (3,874 ) — 30 Total 21,049 — 21,049 (19,388 ) (520 ) 1,141 Liabilities (1) Derivatives 9,013 — 9,013 (7,758 ) (884 ) 371 Payables under repurchase agreements 15,964 — 15,964 (15,847 ) — 117 Payables under securities lending transactions 1,181 — 1,181 (1,179 ) — 2 Total 26,158 — 26,158 (24,784 ) (884 ) 490 September 30, 2018 Assets (1) Derivatives 6,766 — 6,766 (5,409 ) (571 ) 786 Receivables under resale agreements 10,144 — 10,144 (10,075 ) — 69 Receivables under securities borrowing transactions 2,032 — 2,032 (2,009 ) — 23 Total 18,942 — 18,942 (17,493 ) (571 ) 878 Liabilities (1) Derivatives 6,326 — 6,326 (5,069 ) (722 ) 535 Payables under repurchase agreements 17,066 — 17,066 (17,045 ) — 21 Payables under securities lending transactions 1,359 — 1,359 (1,355 ) — 4 Total 24,751 — 24,751 (23,469 ) (722 ) 560 Notes: (1) Amounts relating to master netting arrangements or similar agreements where the MHFG Group does not have the legal right of set-off over-the-counter OTC-cleared (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.

Repurchase agreements and secur

Repurchase agreements and securities lending transactions accounted for as secured borrowings	6 Months Ended
	Sep. 30, 2018
Repurchase agreements and securities lending transactions accounted for as secured borrowings	19. Repurchase agreements and securities lending transactions accounted for as secured borrowings The following table shows the gross amounts of liabilities associated with repurchase agreements and securities lending transactions, by remaining contractual maturity at March 31, 2018 and September 30, 2018: Overnight and Up to 30 days 31-90 days Greater than 90 days Total (in billions of yen) March 31, 2018 Repurchase agreements 255 11,669 3,676 1,057 16,657 Securities lending transactions 1,270 355 — 208 1,833 Total 1,525 12,024 3,676 1,265 18,490 September 30, 2018 Repurchase agreements 4,095 10,198 1,687 1,508 17,488 Securities lending transactions 1,068 771 — 273 2,112 Total 5,163 10,969 1,687 1,781 19,600 The following table shows the gross amounts of liabilities associated with repurchase agreements and securities lending transactions, by class of underlying collateral at March 31, 2018 and September 30, 2018: Repurchase Securities lending (in billions of yen) March 31, 2018 Japanese government bonds and Japanese local government bonds 1,358 592 Foreign government bonds and foreign agency mortgage-backed securities 14,426 303 Commercial paper and corporate bonds 328 48 Equity securities 406 869 Other 139 21 Total (Note) 16,657 1,833 September 30, 2018 Japanese government bonds and Japanese local government bonds 2,365 320 Foreign government bonds and foreign agency mortgage-backed securities 14,157 700 Commercial paper and corporate bonds 383 51 Equity securities 418 1,021 Other 165 20 Total (Note) 17,488 2,112 Note: Amounts exceeded the gross amounts recognized in Note 18 “Offsetting of financial assets and financial liabilities” by ¥1,345 billion and ¥1,175 billion, at March 31, 2018 and September 30, 2018, respectively, which excluded the amounts relating to master netting agreements or similar agreements where the MHFG Group did not have the legal right of set-off The MHFG Group is required to post securities as collateral with a fair value equal to or in excess of the principal amount of the cash borrowed under repurchase agreements. For securities lending transactions, the Group receives collateral in the form of cash. These contracts involve risks, including (1) the counterparty may fail to return the securities at maturity and (2) the fair value of the securities posted may decline below the amount of the Group’s obligation and therefore the counterparty may require additional amounts. The Group attempts to mitigate these risks by entering into transactions mainly with central counterparty clearing houses which revalue assets and perform margin maintenance activities on a daily basis, diversifying the maturities and counterparties, and using mainly highly liquid securities.

Business segment information

Business segment information	6 Months Ended
	Sep. 30, 2018
Business segment information	20. Business segment information The MHFG Group consists of the following five in-house The services that each in-house Retail & Business Banking Company This company provides financial services for individual customers, small and medium-sized Corporate & Institutional Company This company provides financial services for large corporations, financial institutions and public corporations in Japan. Global Corporate Company This company provides financial services for Japanese overseas affiliated corporate customers and non-Japanese Global Markets Company This company invests in financial products with market risk, such as interest rate risk, equity risk, and credit risk. Asset Management Company This company develops financial products and provides financial services that match the asset management needs of its wide range of customers from individuals to institutional investors. The reportable segment information, set forth below, is derived from the internal management reporting systems used by management to measure the performance of the Group’s operating segments. Management measures the performance of each of the operating segments in accordance with internal managerial accounting rules and practices. In addition, the format and information are presented primarily on the basis of Japanese GAAP. Therefore, they are not consistent with the consolidated financial statements prepared in accordance with U.S. GAAP. A reconciliation is provided for the total amount of each business segment’s “Net business profits (losses) + Net gains (losses) related to ETFs and others” with income before income tax expense under U.S. GAAP. Management does not use information on business segment’s assets to allocate resources and assess performance and has not prepared information on the segment’s assets. Accordingly, information on the segment’s assets is not available. MHFG (Consolidated) Six months ended September 30, 2017 (4) Retail & Corporate & Global Global Asset Others (3) Total (in billions of yen) Gross profits + Net gains (losses) related to ETFs and others (1) 343.2 187.6 153.2 239.9 24.8 32.5 981.2 General and administrative expenses 358.9 101.3 121.6 100.3 13.9 15.3 711.3 Equity in earnings (losses) of equity method investees—net 7.5 0.6 1.3 — 0.5 0.7 10.6 Amortization of goodwill and others 0.2 0.2 0.2 1.2 4.0 1.2 7.0 Others — — — — — (10.5 ) (10.5 ) Net business profits (losses) (2) (8.4 ) 86.7 32.7 138.4 7.4 6.2 263.0 MHFG (Consolidated) Six months ended September 30, 2018 (4) Retail & Corporate & Global Global Asset Others (3) Total (in billions of yen) Gross profits + Net gains (losses) related to ETFs and others (1) 345.9 223.7 198.2 237.4 25.0 21.3 1,051.5 General and administrative expenses 360.2 100.3 121.4 103.5 13.9 23.4 722.7 Equity in earnings (losses) of equity method investees—net 14.4 0.6 2.8 — 0.6 1.0 19.4 Amortization of goodwill and others 0.2 0.2 0.2 1.2 4.0 1.0 6.8 Others — — — — — (10.4 ) (10.4 ) Net business profits (losses) (2) (0.1 ) 123.8 79.4 132.7 7.7 (12.5 ) 331.0 Notes: (1) “Gross profits + Net gains (losses) related to ETFs and others” is reported instead of sales reported by general corporations. Gross profits is defined as the sum of net interest income, fiduciary income, net fee and commission income, net trading income and net other operating income. Net gains (losses) related to ETFs and others consist of net gains (losses) on ETFs held by MHBK and MHTB and net gains (losses) on operating investment securities of MHSC on its consolidated basis. For the six months ended September 30, 2017 and 2018, net gains related to ETFs and others amounted to ¥21.4 billion and ¥39.9 billion, respectively, of which ¥13.9 billion and ¥33.6 billion, respectively, are included in “Global Markets Company”. (2) Net business profits is used in Japan as a measure of the profitability of core banking operations. Measurement of net business profits is required for regulatory reporting to the Financial Services Agency. (3) “Others” includes items which should be eliminated as internal transactions between each segment on a consolidated basis. (4) Beginning on April 1, 2018, new allocation methods for transactions between each segment and “Others” have been applied. In connection with the use of the new allocation methods, the presentation of “Net business profits” has changed to “Net business profits (losses) + Net gains (losses) related to ETFs and others”. Before the change, “Net gains (losses) related to ETFs and others” were included in “Gross profits” of each segment and eliminated in “Others”. In addition, “Amortization of goodwill and others” has been presented as a new item. Figures for the six months ended September 30, 2017 have been restated for the new allocation methods. These changes more appropriately reflect the performance of each of the operating segments in accordance with internal managerial accounting rules and practices. Furthermore, income and expenses of foreign branches of MHBK and foreign subsidiaries with functional currency other than Japanese Yen have been translated for purpose of segment reporting using the budgeted foreign currency rates. Prior period comparative amounts for these foreign currency adjustments have been translated using current period budgeted foreign currency rates. Reconciliation As explained above, the measurement bases of the internal management reporting systems and the income and expenses items included are different from the accompanying consolidated statements of income. Therefore, it is impracticable to present reconciliations of all the business segment’s information, other than net business profits, to the corresponding items in the accompanying consolidated statements of income. A reconciliation of “Net business profits (losses) + Net gains (losses) related to ETFs and others” under the internal management reporting systems for the six months ended September 30, 2017 and 2018 presented above to income before income tax expense shown on the consolidated statements of income is as follows: Six months ended September 30, 2017 2018 (in billions of yen) Net business profits (losses) + Net gains (losses) related to ETFs and others 263.0 331.0 Less: Net gains (losses) related to ETFs and others (21.4 ) (39.9 ) U.S. GAAP adjustments 95.7 (160.0 ) (Provision) credit for loan losses 118.0 13.3 Net gains (losses) related to equity investments 100.9 289.5 Non-recurring (3.6 ) 0.9 Gains on disposal of premises and equipment 4.6 4.3 (Provision) credit for losses on off-balance-sheet 4.2 9.9 Others—net (48.5 ) (31.4 ) Income before income tax expense 512.9 417.6

Basis of presentation (Policies

Basis of presentation (Policies)	6 Months Ended
	Sep. 30, 2018
Basis of presentation	1. 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. For a discussion of the Group’s segment information, see Note 20 “Business segment information”. MHFG and its domestic subsidiaries as well as its foreign subsidiaries maintain their accounting records in accordance with the accounting standards of Japan and those standards of the countries in which they are domiciled. Certain adjustments and reclassifications have been incorporated in the accompanying consolidated financial statements to conform them to 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 interim financial reporting period ends on September 30 and certain subsidiaries’ interim financial reporting periods end on June 30. When determining whether to consolidate investee entities, the MHFG Group performed an analysis of the facts and circumstances of the particular relationships between the MHFG Group and the investee entities as well as the 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 in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 810, “Consolidation” (“ASC 810”). All significant intercompany transactions and balances have been eliminated upon consolidation. The MHFG Group accounts for investments in entities over which it has significant influence by 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 Equity in earnings (losses) of equity method investees—net. Certain comparative amounts for the prior period have been reclassified in order to conform to the current year’s presentation. The unaudited consolidated financial statements should be read in conjunction with the audited financial statements and related notes thereto included in the annual financial statements for the fiscal year ended March 31, 2018. Certain financial information that is normally included in annual financial statements prepared in accordance with U.S. GAAP, but is not required for interim reporting purposes, has been condensed or omitted.
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
Definition of cash and cash equivalents	Definition of cash and cash equivalents For purposes of the consolidated statements of cash flows, Cash and cash equivalents consists of Cash and due from banks and Interest-bearing deposits in other banks. Cash deposited with central banks that must be maintained to meet minimum regulatory requirements is classified as restricted cash and included in Cash and cash equivalents. For more information on restricted cash, see Note 9 “Pledged assets and collateral” of MHFG’s Form 20-F for the fiscal year ended March 31, 2018.

Investments (Tables)

Investments (Tables)	6 Months Ended
	Sep. 30, 2018
Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Available-for-Sale and Held-to-Maturity Securities	The amortized cost, gross unrealized gains and losses, and fair value of available-for-sale held-to-maturity Amortized cost Gross unrealized Gross unrealized Fair value (in millions of yen) March 31, 2018 Available-for-sale Debt securities: Japanese government bonds 13,334,619 7,332 9,656 13,332,295 Japanese local government bonds 236,711 2,903 280 239,334 U.S. Treasury bonds and federal agency securities 689,297 109 3,557 685,849 Other foreign government bonds 1,057,852 1,043 1,102 1,057,793 Agency mortgage-backed securities (1) 882,686 13,356 7,628 888,414 Residential mortgage-backed securities 117,870 1,264 281 118,853 Commercial mortgage-backed securities 437,115 4,132 323 440,924 Japanese corporate bonds and other debt securities (2) 1,950,947 40,290 1,410 1,989,827 Foreign corporate bonds and other debt securities (3) 879,506 1,927 2,082 879,351 Equity securities (marketable) (4) 1,595,106 2,449,173 11,291 4,032,988 Total 21,181,709 2,521,529 37,610 23,665,628 Held-to-maturity Debt securities: Japanese government bonds 1,959,910 24,472 — 1,984,382 Agency mortgage-backed securities (5) 557,641 — 20,177 537,464 Total 2,517,551 24,472 20,177 2,521,846 September 30, 2018 Available-for-sale Debt securities: Japanese government bonds 13,468,933 3,947 21,693 13,451,187 Japanese local government bonds 240,193 914 652 240,455 U.S. Treasury bonds and federal agency securities 1,138,917 78 5,204 1,133,791 Other foreign government bonds 1,244,490 557 1,669 1,243,378 Agency mortgage-backed securities (1) 871,031 9,984 10,008 871,007 Residential mortgage-backed securities 108,963 908 434 109,437 Commercial mortgage-backed securities 465,251 3,641 298 468,594 Japanese corporate bonds and other debt securities (2) 2,010,207 30,992 2,356 2,038,843 Foreign corporate bonds and other debt securities (3) 913,328 2,580 985 914,923 Equity securities (marketable) (4) — — — — Total 20,461,313 53,601 43,299 20,471,615 Held-to-maturity Debt securities: Japanese government bonds 1,599,900 19,418 — 1,619,318 Agency mortgage-backed securities (5) 537,111 — 24,153 512,958 Total 2,137,011 19,418 24,153 2,132,276 Notes: (1) Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥742,565 million and ¥145,849 million, respectively, at March 31, 2018, and ¥728,836 million and ¥142,171 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Government National Mortgage Association (“Ginnie Mae”) securities, which are guaranteed by the United States government. (2) Other debt securities presented in this line primarily consist of Japanese negotiable certificates of deposit (“NCDs”), of which the total fair values were ¥106,101 million at March 31, 2018, and ¥104,775 million at September 30, 2018. (3) Other debt securities presented in this line primarily consist of Foreign NCDs and asset-backed securities (“ABS”), of which the total fair values were ¥313,164 million at March 31, 2018, and ¥342,999 million at September 30, 2018. (4) The MHFG Group adopted ASU No.2016-01 available-for-sale (5) All Agency mortgage-backed securities presented in this line are Ginnie Mae securities.
Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities by Contractual Maturity	The amortized cost and fair value of available-for-sale held-to-maturity Amortized cost Due in one Due after one Due after five Due after Total (in millions of yen) Available-for-sale Debt securities: Japanese government bonds 8,373,572 3,722,338 1,063,748 309,275 13,468,933 Japanese local government bonds 29,530 143,921 61,579 5,163 240,193 U.S. Treasury bonds and federal agency securities 1,033,650 — 105,267 — 1,138,917 Other foreign government bonds 970,819 258,152 12,602 2,917 1,244,490 Agency mortgage-backed securities — — — 871,031 871,031 Residential mortgage-backed securities — — — 108,963 108,963 Commercial mortgage-backed securities 1,852 178,690 212,459 72,250 465,251 Japanese corporate bonds and other debt securities 407,643 989,938 427,553 185,073 2,010,207 Foreign corporate bonds and other debt securities 514,374 330,725 65,459 2,770 913,328 Total 11,331,440 5,623,764 1,948,667 1,557,442 20,461,313 Held-to-maturity Debt securities: Japanese government bonds 960,044 479,868 159,988 — 1,599,900 Agency mortgage-backed securities — — — 537,111 537,111 Total 960,044 479,868 159,988 537,111 2,137,011 Fair value Due in one Due after one Due after five Due after Total (in millions of yen) Available-for-sale Debt securities: Japanese government bonds 8,372,894 3,722,825 1,054,008 301,460 13,451,187 Japanese local government bonds 29,558 144,269 61,492 5,136 240,455 U.S. Treasury bonds and federal agency securities 1,033,135 — 100,656 — 1,133,791 Other foreign government bonds 970,233 257,751 12,489 2,905 1,243,378 Agency mortgage-backed securities — — — 871,007 871,007 Residential mortgage-backed securities — — — 109,437 109,437 Commercial mortgage-backed securities 1,852 179,517 214,475 72,750 468,594 Japanese corporate bonds and other debt securities 431,664 991,020 428,321 187,838 2,038,843 Foreign corporate bonds and other debt securities 514,166 332,225 65,762 2,770 914,923 Total 11,353,502 5,627,607 1,937,203 1,553,303 20,471,615 Held-to-maturity Debt securities: Japanese government bonds 961,712 492,560 165,046 — 1,619,318 Agency mortgage-backed securities — — — 512,958 512,958 Total 961,712 492,560 165,046 512,958 2,132,276
Other-Than-Temporary Impairment Losses on Available-for-Sale Securities	The following table shows the other-than-temporary impairment losses on available-for-sale held-to-maturity Six months ended September 30, 2017 2018 (in millions of yen) Available-for-sale Debt securities 1,000 213 Equity securities (Note) 2,521 — Total 3,521 213 Note: Effective April 1, 2018, the available-for-sale
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 a Continuous Unrealized Loss Position	The following table shows 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, 2018 and September 30, 2018: Less than 12 months 12 months or more Total Fair Gross Fair Gross Fair Gross (in millions of yen) March 31, 2018 Available-for-sale Debt securities: Japanese government bonds 8,052,820 3,716 2,868,078 5,940 10,920,898 9,656 Japanese local government bonds 28,827 139 58,998 141 87,825 280 U.S. Treasury bonds and federal agency securities 515,005 3,557 — — 515,005 3,557 Other foreign government bonds 419,648 1,030 68,359 72 488,007 1,102 Agency mortgage-backed securities (1) 45,434 1,116 188,326 6,512 233,760 7,628 Residential mortgage-backed securities 11,336 14 16,129 267 27,465 281 Commercial mortgage-backed securities 68,723 242 7,835 81 76,558 323 Japanese corporate bonds and other debt securities 563,831 933 403,069 477 966,900 1,410 Foreign corporate bonds and other debt securities 358,410 888 87,472 1,194 445,882 2,082 Equity securities (marketable) (2) 338,243 11,249 366 42 338,609 11,291 Total 10,402,277 22,884 3,698,632 14,726 14,100,909 37,610 Held-to-maturity Debt securities: Agency mortgage-backed securities (3) 30,589 766 506,875 19,411 537,464 20,177 Total 30,589 766 506,875 19,411 537,464 20,177 September 30, 2018 Available-for-sale Debt securities: Japanese government bonds 6,763,194 13,798 3,243,600 7,895 10,006,794 21,693 Japanese local government bonds 92,616 329 83,400 323 176,016 652 U.S. Treasury bonds and federal agency securities 961,157 2,107 52,378 3,097 1,013,535 5,204 Other foreign government bonds 704,626 1,023 46,274 646 750,900 1,669 Agency mortgage-backed securities (1) 151,610 782 204,959 9,226 356,569 10,008 Residential mortgage-backed securities 26,351 151 24,883 283 51,234 434 Commercial mortgage-backed securities 44,603 118 42,526 180 87,129 298 Japanese corporate bonds and other debt securities 497,300 1,767 599,554 589 1,096,854 2,356 Foreign corporate bonds and other debt securities 222,267 400 102,586 585 324,853 985 Equity securities (marketable) (2) — — — — — — Total 9,463,724 20,475 4,400,160 22,824 13,863,884 43,299 Held-to-maturity Debt securities: Agency mortgage-backed securities (3) 22,319 827 490,639 23,326 512,958 24,153 Total 22,319 827 490,639 23,326 512,958 24,153 Notes: (1) Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥88,017 million and ¥145,743 million, respectively, at March 31, 2018, and ¥214,480 million and ¥142,089 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Ginnie Mae securities, which are guaranteed by the United States government. (2) The MHFG Group adopted ASU No.2016-01 (3) All Agency mortgage-backed securities presented in this line are Ginnie Mae securities.
Realized Gains and Losses on Sales of Available-for-Sale Securities	The following table shows the realized gains and losses on sales of available-for-sale available-for-sale Six months ended September 30, 2017 2018 (in millions of yen) Gross realized gains 127,360 9,955 (Note) Gross realized losses (10,020 ) (8,497 ) (Note) Net realized gains (losses) on sales of available-for-sale 117,340 1,458 (Note) Note: Effective April 1, 2018, the available-for-sale
Summary of Composition of Other Investments	The following table summarizes the composition of Other investments at March 31, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 (in millions of yen) Equity method investments 280,666 301,524 Investments held by consolidated investment companies 37,735 41,230 Other equity interests 267,495 — (Note) Total 585,896 342,754 Note: In connection with the adoption of ASU No.2016-01, other equity interests are disclosed as Equity securities. See Note 2 “Recently issued accounting pronouncements” for further details.
Summary of Details of Net Gains and Losses on Equity Securities	The following table shows the details of the net gains and losses on Equity securities for the six months ended September 30, 2018: Six months ended 2018 (in millions of yen) Net gains and losses recognized during the period on equity securities 306,788 Less: Net gains and losses recognized during the period on equity securities sold during the period 116,308 Unrealized gains and losses recognized during the reporting period on equity securities still held at the reporting period 190,480
Summary of Equity Securities Without Readily Determinable Fair Values	The following table shows the details of Equity securities without readily determinable fair values, for which the measurement alternative is used, for the six months ended September 30, 2018: Six months ended 2018 (in millions of yen) Carrying amounts at the end of the period 231,810 Downward adjustments and impairments: During the period 976 Cumulative 976 Upward adjustments: During the period 1,837 Cumulative 1,837

Loans (Tables)

Loans (Tables)	6 Months Ended
	Sep. 30, 2018
Loans Outstanding by Domicile and Industry of Borrower	The table below presents loans outstanding by domicile and industry of borrower at March 31, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 (in millions of yen) Domestic: Manufacturing 8,156,341 8,469,440 Construction and real estate 8,101,668 8,475,834 Services 5,024,018 5,288,571 Wholesale and retail 5,112,673 5,168,408 Transportation and communications 3,564,869 3,710,990 Banks and other financial institutions 4,471,423 4,455,338 Government and public institutions 8,882,125 5,776,149 Other industries (Note) 5,018,387 5,059,891 Individuals: Mortgage loans 9,445,286 9,191,280 Other 883,724 867,192 Total domestic 58,660,514 56,463,093 Foreign: Commercial and industrial 17,195,159 19,322,908 Banks and other financial institutions 7,465,140 8,527,586 Government and public institutions 302,891 625,263 Other 37,636 41,699 Total foreign 25,000,826 28,517,456 Total 83,661,340 84,980,549 Less: Unearned income and deferred loan fees—net 146,696 150,301 Total loans before allowance for loan losses 83,514,644 84,830,248 Note: Other industries of Domestic includes trade receivables and lease receivables of consolidated VIEs.
Credit Quality Information of Loans Based on MHFG Group's Internal Rating System	The table below presents credit quality information of loans based on the MHFG Group’s internal rating system at March 31, 2018 and September 30, 2018: Normal obligors Watch obligors (1) Corporate Retail (2) Other (3) Corporate Retail (2) Other (3) Impaired Total (in millions of yen) March 31, 2018 Domestic: Manufacturing 7,705,495 77,947 23,343 197,465 9,775 246 142,070 8,156,341 Construction and real estate 7,317,972 541,778 13,332 172,287 15,466 — 40,833 8,101,668 Services 4,535,793 172,045 141,718 95,223 21,109 55 58,075 5,024,018 Wholesale and retail 4,636,236 177,965 17,305 121,832 27,975 476 130,884 5,112,673 Transportation and communications 3,414,781 76,532 1,774 35,339 8,916 — 27,527 3,564,869 Banks and other financial institutions 4,244,101 1,640 196,431 16,716 194 — 12,341 4,471,423 Government and public institutions 3,010,708 — 5,871,417 — — — — 8,882,125 Other industries (4) 2,716,502 3,536 2,170,442 2,708 259 121,201 3,739 5,018,387 Individuals 222,410 9,822,244 88,044 23,491 81,550 1,109 90,162 10,329,010 Total domestic 37,803,998 10,873,687 8,523,806 665,061 165,244 123,087 505,631 58,660,514 Foreign: Commercial and industrial 14,192,930 209 2,432,189 398,231 — 64,950 106,650 17,195,159 Banks and other financial institutions 6,949,036 — 487,978 28,126 — — — 7,465,140 Government and public institutions 301,072 — — — — — 1,819 302,891 Other 1,906 9,245 23,730 242 6 1,347 1,160 37,636 Total foreign 21,444,944 9,454 2,943,897 426,599 6 66,297 109,629 25,000,826 Total 59,248,942 10,883,141 11,467,703 1,091,660 165,250 189,384 615,260 83,661,340 September 30, 2018 Domestic: Manufacturing 8,130,139 72,651 15,714 124,530 8,305 522 117,579 8,469,440 Construction and real estate 7,709,697 522,815 10,358 178,226 15,083 — 39,655 8,475,834 Services 4,731,189 168,384 206,848 91,898 18,863 — 71,389 5,288,571 Wholesale and retail 4,694,532 169,576 17,496 132,233 27,000 489 127,082 5,168,408 Transportation and communications 3,558,659 73,437 529 39,194 8,313 — 30,858 3,710,990 Banks and other financial institutions 4,236,485 1,741 184,392 23,084 265 — 9,371 4,455,338 Government and public institutions 2,594,132 — 3,182,017 — — — — 5,776,149 Other industries (4) 2,888,378 2,996 2,148,915 8,346 375 5,447 5,434 5,059,891 Individuals 226,932 9,579,329 67,290 20,700 76,161 1,144 86,916 10,058,472 Total domestic 38,770,143 10,590,929 5,833,559 618,211 154,365 7,602 488,284 56,463,093 Foreign: Commercial and industrial 16,430,107 116 2,431,047 341,687 — 43,503 76,448 19,322,908 Banks and other financial institutions 7,988,472 — 515,716 23,389 — — 9 8,527,586 Government and public institutions 623,460 — — — — — 1,803 625,263 Other 8,271 9,024 21,527 342 65 1,170 1,300 41,699 Total foreign 25,050,310 9,140 2,968,290 365,418 65 44,673 79,560 28,517,456 Total 63,820,453 10,600,069 8,801,849 983,629 154,430 52,275 567,844 84,980,549 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) Non-impaired (4) Other industries of Domestic includes trade receivables and lease receivables of consolidated VIEs.
Impaired Loans Information	The table below presents impaired loans information at March 31, 2018 and September 30, 2018: Recorded investment (1) Requiring Not (2) Total Unpaid Related (3) Average Interest (4) (in millions of yen) March 31, 2018 Domestic: Manufacturing 135,083 6,987 142,070 146,857 45,750 218,899 1,869 Construction and real estate 31,557 9,276 40,833 48,752 4,411 49,926 516 Services 48,691 9,384 58,075 64,348 13,305 60,198 919 Wholesale and retail 119,463 11,421 130,884 139,556 42,798 139,333 1,842 Transportation and communications 25,019 2,508 27,527 28,480 6,862 25,672 370 Banks and other financial institutions 8,392 3,949 12,341 12,341 3,176 8,648 78 Other industries 3,650 89 3,739 3,869 3,563 4,537 53 Individuals 43,326 46,836 90,162 95,338 4,315 97,404 1,402 Total domestic 415,181 90,450 505,631 539,541 124,180 604,617 7,049 Foreign: Total foreign (5) 63,346 46,283 109,629 125,329 28,333 151,588 1,042 Total 478,527 136,733 615,260 664,870 152,513 756,205 8,091 Recorded investment (1) Requiring Not (2) Total Unpaid Related (3) Average Interest (4) (in millions of yen) September 30, 2018 Domestic: Manufacturing 111,026 6,553 117,579 122,029 40,969 129,824 714 Construction and real estate 30,818 8,837 39,655 47,362 4,032 40,244 240 Services 62,557 8,832 71,389 76,953 17,226 64,732 493 Wholesale and retail 117,212 9,870 127,082 136,833 39,610 128,983 905 Transportation and communications 28,043 2,815 30,858 31,814 8,688 29,193 198 Banks and other financial institutions 5,545 3,826 9,371 9,371 813 10,856 47 Other industries 5,357 77 5,434 5,565 4,000 4,586 15 Individuals 40,982 45,934 86,916 91,775 2,985 88,539 642 Total domestic 401,540 86,744 488,284 521,702 118,323 496,957 3,254 Foreign: Total foreign (5) 32,591 46,969 79,560 93,212 13,857 94,595 517 Total 434,131 133,713 567,844 614,914 132,180 591,552 3,771 Notes: (1) Amounts represent the outstanding balances of nonaccrual loans. The MHFG Group’s policy for placing loans in nonaccrual status 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 the allowance for groups of loans which were collectively evaluated for impairment, in addition to the allowance for those loans that were individually evaluated for impairment. The total carrying amount of the groups of loans which were collectively evaluated for impairment at March 31, 2018 and September 30, 2018 was ¥245,809 million and ¥252,407 million, respectively. (4) Amounts represent the amount of interest income on impaired loans recognized on a cash basis and included in Interest income on loans in the consolidated statements of income. (5) The majority of Total foreign consist of Commercial and Industrial loans.
Troubled Debt Restructurings Entered Modified Periods by Type of Concession Granted	obligor rating is E2 or below. The following table presents modified loans that were determined to be TDRs during the six months ended September 30, 2017 and 2018: Loan forgiveness or debt to equity swaps Interest rate reduction Recorded investment (1) Charge-offs (in millions of yen) September 30, 2017 Domestic: Manufacturing — — 55,611 Construction and real estate — — 9,045 Services — — 18,740 Wholesale and retail — — 74,625 Transportation and communications — — 12,244 Banks and other financial institutions — — 3,461 Individuals — — 7,619 Total domestic — — 181,345 Foreign: Total foreign (2) — — 13,303 Total — — 194,648 September 30, 2018 Domestic: Manufacturing — — 51,161 Construction and real estate — — 7,764 Services — — 29,203 Wholesale and retail — — 75,593 Transportation and communications — — 13,999 Banks and other financial institutions — — 7,160 Individuals — — 8,866 Total domestic — — 193,746 Foreign: Total foreign (2) 1,008 2,012 9,493 Total 1,008 2,012 203,239 Notes: (1) Amounts represent the book values of loans immediately after the restructurings. (2) The majority of Total foreign consist of Commercial and Industrial loans.
Payment Defaults Occurred During Periods with Respect to Loans Modified as Troubled Debt Restructurings within Previous Six Months	bankrupt. The following table presents payment defaults which occurred during the six months ended September 30, 2017 and 2018 with respect to the loans modified as TDRs within the previous twelve months: Recorded investment September 30, 2017 September 30, 2018 (in millions of yen) Domestic: Manufacturing 2,006 383 Construction and real estate 70 390 Services 2,561 714 Wholesale and retail 13,396 6,700 Transportation and communications 201 409 Other industries 130 — Individuals 904 2,241 Total domestic 19,268 10,837 Foreign: Total foreign 4,588 — Total 23,856 10,837
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, 2018 and September 30, 2018: 30-59 days 60-89 days 90 days or Total past Current Total (in millions of yen) March 31, 2018 Domestic: Manufacturing 585 470 8,037 9,092 8,147,249 8,156,341 Construction and real estate 1,641 474 28,633 30,748 8,070,920 8,101,668 Services 1,977 1,142 5,051 8,170 5,015,848 5,024,018 Wholesale and retail 1,704 1,083 6,639 9,426 5,103,247 5,112,673 Transportation and communications 356 639 1,828 2,823 3,562,046 3,564,869 Banks and other financial institutions — 1,301 — 1,301 4,470,122 4,471,423 Government and public institutions — — — — 8,882,125 8,882,125 Other industries 33 12 37 82 5,018,305 5,018,387 Individuals 31,566 12,426 31,444 75,436 10,253,574 10,329,010 Total domestic 37,862 17,547 81,669 137,078 58,523,436 58,660,514 Foreign: Total foreign (Note) 897 450 41,316 42,663 24,958,163 25,000,826 Total 38,759 17,997 122,985 179,741 83,481,599 83,661,340 September 30, 2018 Domestic: Manufacturing 594 416 7,714 8,724 8,460,716 8,469,440 Construction and real estate 1,461 927 26,369 28,757 8,447,077 8,475,834 Services 1,006 1,014 4,121 6,141 5,282,430 5,288,571 Wholesale and retail 2,829 833 6,626 10,288 5,158,120 5,168,408 Transportation and communications 53 707 1,563 2,323 3,708,667 3,710,990 Banks and other financial institutions 90 6 — 96 4,455,242 4,455,338 Government and public institutions — — — — 5,776,149 5,776,149 Other industries — — 45 45 5,059,846 5,059,891 Individuals 29,699 12,522 31,885 74,106 9,984,366 10,058,472 Total domestic 35,732 16,425 78,323 130,480 56,332,613 56,463,093 Foreign: Total foreign (Note) 876 348 40,843 42,067 28,475,389 28,517,456 Total 36,608 16,773 119,166 172,547 84,808,002 84,980,549 Note: The majority of Total foreign consist of Commercial and Industrial loans.

Allowance for loan losses (Tabl

Allowance for loan losses (Tables)	6 Months Ended
	Sep. 30, 2018
Changes in Allowance for Loan Losses, Allowance for Loan Losses and Loans Outstanding Disaggregated on Basis of Impairment Method, by Portfolio Segment	Changes in Allowance for loan losses by portfolio segment for the six months ended September 30, 2017 and 2018 are shown below: Corporate Retail Other Total (in millions of yen) Six months ended September 30, 2017 Balance at beginning of period 407,327 36,923 35,423 479,673 Provision (credit) for loan losses (109,379 ) (6,469 ) (2,114 ) (117,962 ) Charge-offs (17,366 ) (745 ) (3,107 ) (21,218 ) Recoveries 6,447 315 1,247 8,009 Net charge-offs (10,919 ) (430 ) (1,860 ) (13,209 ) Others (Note) 2,552 — (585 ) 1,967 Balance at end of period 289,581 30,024 30,864 350,469 Six months ended September 30, 2018 Balance at beginning of period 249,072 28,192 32,638 309,902 Provision (credit) for loan losses (13,435 ) (2,290 ) 2,445 (13,280 ) Charge-offs (27,419 ) (1,243 ) (2,602 ) (31,264 ) Recoveries 4,914 220 2,409 7,543 Net charge-offs (22,505 ) (1,023 ) (193 ) (23,721 ) Others (Note) 2,519 — (931 ) 1,588 Balance at end of period 215,651 24,879 33,959 274,489 Note: Others includes primarily foreign exchange translation. The table below presents Allowance for loan losses and loans outstanding by portfolio segment disaggregated on the basis of impairment method at March 31, 2018 and September 30, 2018: Corporate Retail Other Total (in millions of yen) March 31, 2018 Allowance for loan losses 249,072 28,192 32,638 309,902 of which individually evaluated for impairment 129,789 2,602 7,383 139,774 of which collectively evaluated for impairment 119,283 25,590 25,255 170,128 Loans (Note) 60,837,559 11,133,862 11,689,919 83,661,340 of which individually evaluated for impairment 593,053 21,364 61,023 675,440 of which collectively evaluated for impairment 60,244,506 11,112,498 11,628,896 82,985,900 September 30, 2018 Allowance for loan losses 215,651 24,879 33,959 274,489 of which individually evaluated for impairment 105,988 2,501 6,954 115,443 of which collectively evaluated for impairment 109,663 22,378 27,005 159,046 Loans (Note) 65,256,236 10,837,056 8,887,257 84,980,549 of which individually evaluated for impairment 474,645 21,723 45,420 541,788 of which collectively evaluated for impairment 64,781,591 10,815,333 8,841,837 84,438,761 Note: Amounts represent loan balances before deducting unearned income and deferred loan fees.

Other assets and liabilities (T

Other assets and liabilities (Tables)	6 Months Ended
	Sep. 30, 2018
Details of Other Assets and Liabilities	The following table sets forth the details of other assets and liabilities at March 31, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 (in millions of yen) Other assets: Accounts receivable: Receivables from brokers, dealers and customers for securities transactions (1) 1,578,952 1,356,005 Other 368,030 364,631 Collateral pledged: Collateral pledged for derivative transactions 981,390 868,572 Margins provided for futures contracts 142,156 171,927 Other 965,137 906,646 Prepaid pension cost 874,191 859,484 Security deposits 126,001 125,739 Loans held for sale 86,153 15,758 Other 609,624 557,763 Total 5,731,634 5,226,525 Other liabilities: Accounts payable: Payables to brokers, dealers and customers for securities transactions (1) 1,410,785 1,986,580 Other 455,789 556,064 Guaranteed trust principal (2) 761,685 780,619 Collateral accepted: Collateral accepted for derivative transactions 598,524 700,758 Margins accepted for futures contracts 325,038 333,238 Unearned income (3) 130,916 132,364 Other 1,022,858 905,459 Total 4,705,595 5,395,082 Notes: (1) Receivables from brokers, dealers and customers for securities transactions included ¥372,395 million and ¥372,799 million of such receivables of consolidated VIEs at March 31, 2018 and September 30, 2018, respectively. Payables to brokers, dealers and customers for securities transactions included ¥422,060 million and ¥446,935 million of such payables of consolidated VIEs at March 31, 2018 and September 30, 2018, respectively. (2) Guaranteed trust principal is the liability of certain consolidated trust arrangements that meet the definition of a VIE for which the MHFG Group provides guarantees for the repayment of principal. See Note 15 “Variable interest entities and securitizations” for further discussion of the guaranteed principal money trusts. (3) Unearned income is primarily comprised of loan fees received from consumer loan customers when loans are made. This income is being deferred and recognized in earnings over the life of the loan.

Preferred and common stock (Tab

Preferred and common stock (Tables)	6 Months Ended
	Sep. 30, 2018
Preferred stock
Schedule of Stock by Class	The composition of preferred stock at March 31, 2018 and September 30, 2018 is as follows: Class of stock March 31, 2018 September 30, 2018 Authorized Issued Authorized Issued (number of shares) Class XIV preferred stock 900,000,000 — 900,000,000 — Class XV preferred stock 900,000,000 — 900,000,000 — Class XVI preferred stock 1,500,000,000 — 1,500,000,000 —
Common Stock
Schedule of Stock by Class	The following table shows the changes in the number of issued shares of common stock during the fiscal year ended March 31, 2018 and the six months ended September 30, 2018: March 31, 2018 September 30, 2018 (number of shares) Balance at beginning of period 25,386,307,945 25,389,644,945 Issuance of new shares of common stock due to exercise of stock acquisition rights 3,337,000 2,854,000 Balance at end of period 25,389,644,945 25,392,498,945

Accumulated other comprehensi_2

Accumulated other comprehensive income (Tables)	6 Months Ended
	Sep. 30, 2018
Changes in Each Component of AOCI	Changes in each component of AOCI for the six months ended September 30, 2017 and 2018 are as follows: Six months ended September 30, 2017 2018 (in millions of yen) AOCI, balance at beginning of period, previously reported 1,521,163 1,741,894 Cumulative effect of change in accounting principles (Note 2) — (1,535,142 ) AOCI, balance at beginning of period, adjusted 1,521,163 206,752 Net unrealized gains (losses) on available-for-sale Balance at beginning of period, previously reported 1,461,302 1,556,585 Cumulative effect of change in accounting principles (Note 2) — (1,525,064 ) Balance at beginning of period, adjusted 1,461,302 31,521 Unrealized holding gains (losses) during period 247,493 (25,155 ) Less: reclassification adjustments for losses (gains) included in net income (78,659 ) (862 ) Change during period 168,834 (26,017 ) Balance at end of period 1,630,136 5,504 Foreign currency translation adjustments: Balance at beginning of period (5,535 ) (35,076 ) Foreign currency translation adjustments during period (4,322 ) 7,678 Less: reclassification adjustments for losses (gains) included in net income — — Change during period (4,322 ) 7,678 Balance at end of period (9,857 ) (27,398 ) Pension liability adjustments: Balance at beginning of period 65,396 220,385 Unrealized gains (losses) during period 32 (218 ) Less: reclassification adjustments for losses (gains) included in net income 140 (2,916 ) Change during period 172 (3,134 ) Balance at end of period 65,568 217,251 Own credit risk adjustments (Note) Balance at beginning of period, previously reported — — Cumulative effect of change in accounting principles (Note 2) — (10,078 ) Balance at beginning of period, adjusted — (10,078 ) Unrealized gains (losses) during period — 2,656 Less: reclassification adjustments for losses (gains) included in net income — (20 ) Change during period — 2,636 Balance at end of period — (7,442 ) Total other comprehensive income (loss), net of tax attributable to MHFG shareholders 164,684 (18,837 ) AOCI, balance at end of period 1,685,847 187,915 Note: The MHFG Group adopted ASU No.2016-01 on April 1, 2018. The ASU requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. See Note 2 “Recently issued accounting pronouncements” for further details.
Amounts Reclassified Out of Accumulated Other Comprehensive Income into Net Income	The following table shows the amounts reclassified out of AOCI into net income during the six months ended September 30, 2018: Six months ended September 30, 2018 Before tax (1) Tax effect (2) Net of tax before Net of tax attributable to (2) Net of tax attributable to shareholders (in millions of yen) Amounts reclassified out of AOCI into net income: Affected line items in the consolidated statements of income: Net unrealized gains (losses) on available-for-sale 1,245 (383 ) 862 — 862 Investment gains (losses)—net Pension liability adjustments 4,102 (1,184 ) 2,918 (2 ) 2,916 Salaries and employee benefits Own credit risk adjustments 29 (9 ) 20 — 20 Other noninterest income (expenses) Total 5,376 (1,576 ) 3,800 (2 ) 3,798 Notes: (1) The amounts in the Before tax column are recorded in each account presented under the heading “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 (loss) attributable to noncontrolling interests in the consolidated statements of income, respectively.

Regulatory matters (Tables)

Regulatory matters (Tables)	6 Months Ended
	Sep. 30, 2018
Capital Adequacy Ratios of MHFG, MHBK, and MHTB Calculated in Accordance with Japanese GAAP and Guidelines Established by Financial Services Agency	Capital adequacy ratios of MHFG, MHBK, and MHTB as of March 31, 2018 and September 30, 2018 calculated in accordance with Japanese GAAP and the guidelines established by the Financial Services Agency are set forth in the following table: March 31, 2018 September 30, 2018 Amount Ratio Amount Ratio (in billions of yen, except percentages) Consolidated: MHFG: Common Equity Tier 1 capital: Required (Note) 4,247 7.135 4,304 7.145 Actual 7,437 12.49 7,607 12.62 Tier 1 capital: Required (Note) 5,140 8.635 5,208 8.645 Actual 9,192 15.44 9,435 15.66 Total risk-based capital: Required (Note) 6,331 10.635 6,413 10.645 Actual 10,860 18.24 11,214 18.61 MHBK: Common Equity Tier 1 capital: Required 2,400 4.50 2,470 4.50 Actual 6,584 12.34 6,817 12.41 Tier 1 capital: Required 3,200 6.00 3,294 6.00 Actual 8,330 15.61 8,638 15.73 Total risk-based capital: Required 4,267 8.00 4,391 8.00 Actual 9,881 18.52 10,331 18.82 MHTB: Common Equity Tier 1 capital: Required 112 4.50 111 4.50 Actual 498 19.99 522 21.25 Tier 1 capital: Required 149 6.00 147 6.00 Actual 499 20.05 523 21.27 Total risk-based capital: Required 199 8.00 196 8.00 Actual 505 20.28 527 21.46 Non-consolidated: MHBK: Common Equity Tier 1 capital: Required 2,312 4.50 2,374 4.50 Actual 6,330 12.32 6,495 12.31 Tier 1 capital: Required 3,082 6.00 3,165 6.00 Actual 8,081 15.73 8,322 15.77 Total risk-based capital: Required 4,109 8.00 4,220 8.00 Actual 9,619 18.72 10,007 18.97 MHTB: Common Equity Tier 1 capital: Required 112 4.50 110 4.50 Actual 504 20.28 520 21.26 Tier 1 capital: Required 149 6.00 147 6.00 Actual 504 20.28 520 21.26 Total risk-based capital: Required 199 8.00 196 8.00 Actual 509 20.50 524 21.45 Note: The required ratios disclosed above, at March 31, 2018 and September 30, 2018, include the transitional capital conservation buffer of 1.875%, the countercyclical capital buffer of 0.01% and 0.02%, respectively, and the transitional additional loss absorbency requirements for global systemically important banks (“G-SIBs”) (“D-SIBs”)

Earnings per common share (Tabl

Earnings per common share (Tables)	6 Months Ended
	Sep. 30, 2018
Computation of Basic and Diluted Earnings Per Common Share	The following table sets forth the computation of basic and diluted earnings per common share for the six months ended September 30, 2017 and 2018: Six months ended September 30, 2017 2018 (in millions of yen) Net income: Net income attributable to MHFG common shareholders 372,549 285,270 Effect of dilutive securities — — Net income attributable to common shareholders after assumed conversions 372,549 285,270 Six months ended September 30, 2017 2018 (thousands of shares) Shares: Weighted average common shares outstanding 25,366,347 25,363,167 Effect of dilutive securities: Stock options 7,933 4,790 Weighted average common shares after assumed conversions 25,374,280 25,367,957 Six months ended September 30, 2017 2018 (in yen) Amounts per common share: Basic net income per common share 14.69 11.25 Diluted net income per common share 14.68 11.25

Income taxes (Tables)

Income taxes (Tables)	6 Months Ended
	Sep. 30, 2018
Components of Income Tax Expense	The following table presents the components of Income tax expense for the six months ended September 30, 2017 and 2018: Six months ended September 30, 2017 2018 (in millions of yen) Current tax expense 99,238 114,666 Deferred tax expense (benefit) 20,095 (28,961 ) Total income tax expense 119,333 85,705
Detailed Amounts of Tax Effects of Items Recorded Directly in Equity	The preceding table does not reflect the tax effects of items recorded directly in Equity for the six months ended September 30, 2017 and 2018. The detailed amounts recorded directly in Equity are as follows: Six months ended September 30, 2017 2018 (in millions of yen) Net unrealized gains (losses) on available-for-sale Unrealized gains (losses) 105,819 (11,292 ) Less: reclassification adjustments (35,053 ) (383 ) Total 70,766 (11,675 ) Pension liability adjustments: Unrealized gains (losses) 11 (97 ) Less: reclassification adjustments 96 (1,184 ) Total 107 (1,281 ) Own credit risk adjustments (Note) Unrealized gains (losses) — 967 Less: reclassification adjustments — (9 ) Total — 958 Total tax effect before allocation to noncontrolling interests 70,873 (11,998 ) Note: The MHFG Group adopted ASU No.2016-01 on April 1, 2018. The ASU requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. See Note 2 “Recently issued accounting pronouncements” for further details.

Pension and other employee be_2

Pension and other employee benefit plans (Tables)	6 Months Ended
	Sep. 30, 2018
Components of Net Periodic Benefit Cost of Severance Indemnities and Pension Plans	The following table summarizes the components of net periodic benefit cost of the severance indemnities and pension plans of the MHFG Group for the six months ended September 30, 2017 and 2018: Six months ended September 30, 2017 2018 (in millions of yen) Service cost-benefits earned during the period 21,643 21,726 Interest costs on projected benefit obligations 3,609 3,331 Expected return on plan assets (17,353 ) (19,124 ) Amortization of prior service benefits 102 76 Amortization of net actuarial loss (gain) 214 (3,942 ) Special termination benefits 2,128 1,792 Net periodic benefit cost 10,343 3,859

Derivative financial instrume_2

Derivative financial instruments (Tables)	6 Months Ended
	Sep. 30, 2018
Summary of Notional and Fair Value Amounts of Derivative Instruments Outstanding	The following table summarizes the notional and fair value amounts of derivative instruments outstanding as of March 31, 2018 and September 30, 2018. The fair values of derivatives are presented on a gross basis, derivative receivables and payables are not offset. In addition, they are not offset against the amounts recognized for 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) March 31, 2018 Notional amount (1) Designated Not designated Designated Not designated (in billions of yen) Interest rate contracts 1,004,169 — 7,176 — 7,143 Foreign exchange contracts 155,832 2 2,695 — 2,382 Equity-related contracts 6,189 — 197 9 142 Credit-related contracts 2,708 — 18 — 21 Other contracts 335 — 23 — 19 Total 1,169,233 2 10,109 9 9,707 Fair value Derivative receivables (2) Derivative payables (2) September 30, 2018 Notional amount (1) Designated Not designated Designated Not designated (in billions of yen) Interest rate contracts 1,057,838 — 4,607 — 4,520 Foreign exchange contracts 152,512 — 2,367 — 2,134 Equity-related contracts 6,201 — 315 — 214 Credit-related contracts 2,909 — 22 — 22 Other contracts 356 — 49 — 46 Total 1,219,816 — 7,360 — 6,936 Notes: (1) Notional amount includes 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.
Summary of Notional and Fair Value Amounts of Credit Derivatives	The following table summarizes the notional and fair value amounts of credit derivatives at March 31, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 Notional amount Fair value Notional amount Fair value (in billions of yen) Credit protection written: Investment grade 1,105 15 1,182 14 Non-investment 197 4 252 5 Total 1,302 19 1,434 19 Credit protection purchased 1,541 (22 ) 1,627 (19 ) 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 - non-investment Non-investment
Maximum Potential Amount of Future Payments for Credit Protection Written by Expiration Period	The following table shows the maximum potential amount of future payments for credit protection written by expiration period at March 31, 2018 and September 30, 2018: Maximum payout/Notional amount March 31, 2018 September 30, 2018 (in billions of yen) One year or less 329 322 After one year through five years 831 927 After five years 142 185 Total 1,302 1,434 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 effect of any amounts that the Group may possibly collect on the underlying assets and the related cash flows, nor netted against that of credit protection purchased.
Quantitative Information about Derivative Instruments with Credit-risk-related Contingent Features	The following table shows the quantitative information about derivative instruments with credit-risk-related contingent features at March 31, 2018 and September 30, 2018: March 31, 2018 September 30, 2018 (in billions of yen) Aggregate fair value of derivative instruments with credit-risk-related contingent features in net liability positions 572 548 Collateral provided to counterparties in the normal course of business 593 514 Amount required to be posted as collateral or settled immediately if credit-risk-related contingent features were triggered (Note) — 34 Note: There was no amount that the Group would be required to post as collateral or settle immediately on March 31, 2018.
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 six months ended September 30, 2017 and 2018: Gains (losses) recorded in income 2017 2018 (in millions of yen) Interest rate contracts 26,648 (75,324 ) Foreign exchange contracts (4,511 ) 26,706 Equity-related contracts (1) (41,869 ) 20,432 Credit-related contracts (2) (3,371 ) (35 ) Other contracts 494 (785 ) Total (22,609 ) (29,006 ) 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 gain (loss) of ¥(273) million and ¥(215) million on the credit derivatives economically managing the credit risk of loans during the six months ended September 30, 2017 and 2018, respectively.
Fair Value Hedging | Designated as Hedging Instrument
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 six months ended September 30, 2017: Gains (losses) recorded in income Six months ended September 30, 2017 Derivatives Hedged Hedge Net gain (loss) excluded (in millions of yen) Equity-related contracts (22,493 ) 20,208 — (2,285 ) Total (22,493 ) 20,208 — (2,285 )
Net Investment Hedging | Designated as Hedging Instrument
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance	The following table summarizes gains and losses information related to net investment hedges for the six months ended September 30, 2017 and 2018: Gains (losses) recorded in income and other comprehensive income (“OCI”) 2017 2018 Effective portion Ineffective portion Effective portion Ineffective portion (in millions of yen) Financial instruments hedging foreign exchange risk 3,487 196 1,937 (32 ) Total 3,487 196 1,937 (32 ) Note: Related to the effective portion of net investment hedges, gains of ¥186 million were reclassified from Accumulated other comprehensive income to earnings for the six months ended September 30, 2018. No amount related to the effective portion of net investment hedges was reclassified from Accumulated other comprehensive income to earnings for the six months ended September 30, 2017.

Commitments and contingencies (

Commitments and contingencies (Tables)	6 Months Ended
	Sep. 30, 2018
Summary of Maximum Potential Amount of Future Payments under Guarantees	The table below summarizes the maximum potential amount of future payments by type of guarantee at March 31, 2018 and September 30, 2018. The maximum potential amount of future payments disclosed below represents the contractual amounts that could be required to 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. March 31, September 30, (in billions of yen) Performance guarantees 2,165 2,205 Guarantees on loans 241 393 Guarantees on securities 164 173 Other guarantees 2,210 2,076 Guarantees for the repayment of trust principal 709 754 Liabilities of trust accounts 13,861 12,172 Derivative financial instruments 11,654 12,941
Summary of Contractual Amounts with Regard to Undrawn Commitments	The table below summarizes the contractual amounts with regard to these undrawn commitments at March 31, 2018 and September 30, 2018: March 31, September 30, (in billions of yen) Commitments to extend credit (Note) 78,448 82,194 Commercial letters of credit 690 817 Total 79,138 83,011 Note: Commitments to extend credit include commitments to invest in securities.
Performance guarantees, Guarantees on loans, Guarantees on securities and Other guarantees
Summary of Maximum Potential Amount of Future Payments under Guarantees	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, 2018 and September 30, 2018: March 31, September 30, (in billions of yen) Investment grade 3,930 3,964 Non-investment 850 883 Total 4,780 4,847 Note: Investment grade in the internal rating scale generally corresponds to BBB- or above in the external rating scale.

Variable interest entities an_2

Variable interest entities and securitizations (Tables)	6 Months Ended
	Sep. 30, 2018
Schedule of Variable Interest Entities	The table below shows the 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, 2018 and September 30, 2018: Consolidated VIEs Significant March 31, 2018 Consolidated assets Total assets Maximum (in billions of yen) Asset-backed commercial paper/loan programs 2,185 — — Asset-backed securitizations 627 78 5 Investments in securitization products 374 — — Investment funds 2,661 1,891 533 Trust arrangements and other 21 — — Total 5,868 1,969 538
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 significant unconsolidated VIEs, as of March 31, 2018 and September 30, 2018: Assets on balance sheets related to unconsolidated VIEs: March 31, 2018 September 30, 2018 (in billions of yen) Trading account assets 89 95 Investments 210 136 Loans 163 133 Total 462 364 Liabilities on balance sheets and maximum exposure to loss related to unconsolidated VIEs: March 31, 2018 September 30, 2018 (in billions of yen) Payables under securities lending transactions 38 42 Trading account liabilities 1 1 Total 39 43 Maximum exposure to loss (Note) 538 445 Note: This represents the maximum amount the Group could possibly be required to record in its consolidated statements of income associated with on-balance-sheet off-balance-sheet

Noninterest income (Tables)

Noninterest income (Tables)	6 Months Ended
	Sep. 30, 2018
Summary of Noninterest Income	Details of Noninterest income for the six months ended September 30, 2017 and 2018 are as follows: Six months ended September 30, 2017 2018 (in millions of yen) Fee and commission income: Securities-related business (1) 85,897 79,138 Deposits and lending business (2) 65,081 70,647 Remittance business (1) 54,166 55,078 Asset management business (1) 50,322 49,818 Trust related business (1) 54,367 57,372 Agency business (1) 18,261 19,509 Guarantee related business (3) 13,899 14,234 Fees for other customer services (1) 59,238 67,931 Total Fee and commission income 401,231 413,727 Foreign exchange gains (losses)—net (3) 50,765 44,718 Trading account gains (losses)—net (2) 235,339 64,956 Investment gains (losses)—net: Debt securities (3) 16,099 2,485 Equity securities (3) 109,390 306,788 Equity in earnings (losses) of equity method investees—net (3) 10,389 22,627 Gains on disposal of premises and equipment (3) 4,567 4,305 Other noninterest income (2) 33,158 48,950 Total 860,938 908,556 Notes: (1) These amounts are revenues from contracts within the scope of ASC 606, “Revenue from contracts with customers” (“ASC 606”). (2) Part of these amounts are considered to be revenues from contracts that are within the scope of ASC 606. (3) These amounts are revenues from contracts that do not meet the scope of ASC 606.

Fair value (Tables)

Fair value (Tables)	6 Months Ended
	Sep. 30, 2018
Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis, Including Fair Value Option Elected	Assets and liabilities measured at fair value on a recurring basis at March 31, 2018 and September 30, 2018, including those for which the MHFG Group has elected the fair value option, are summarized below: March 31, 2018 Level 1 Level 2 Level 3 Assets/ (in billions of yen) Assets: Trading securities (1) Japanese government bonds 1,375 43 — 1,418 Japanese local government bonds — 107 — 107 U.S. Treasury bonds and federal agency securities 2,442 209 — 2,651 Other foreign government bonds 1,682 480 — 2,162 Agency mortgage-backed securities — 1,799 — 1,799 Residential mortgage-backed securities — — 12 12 Certificates of deposit and commercial paper — 643 — 643 Corporate bonds and other 25 1,992 1,013 3,030 Equity securities 1,642 — 23 1,665 Trading securities measured at net asset value (2) 705 Derivative financial instruments: Interest rate contracts 39 7,089 48 7,176 Foreign exchange contracts 17 2,667 13 2,697 Equity-related contracts 82 110 5 197 Credit-related contracts — 16 2 18 Other contracts 6 8 9 23 Available-for-sale Japanese government bonds 12,435 897 — 13,332 Japanese local government bonds — 239 — 239 U.S. Treasury bonds and federal agency securities 686 — — 686 Other foreign government bonds 355 703 — 1,058 Agency mortgage-backed securities — 889 — 889 Residential mortgage-backed securities — 65 54 119 Commercial mortgage-backed securities — — 441 441 Japanese corporate bonds and other debt securities — 1,827 163 1,990 Foreign corporate bonds and other debt securities — 799 80 879 Equity securities (marketable) (3) 3,912 121 — 4,033 Other investments — — 38 38 Total assets measured at fair value on a recurring basis 24,698 20,703 1,901 48,007 Liabilities: Trading securities sold, not yet purchased 2,777 618 4 3,399 Derivative financial instruments: Interest rate contracts 42 7,074 27 7,143 Foreign exchange contracts 11 2,370 1 2,382 Equity-related contracts 81 69 1 151 Credit-related contracts — 20 1 21 Other contracts 4 6 9 19 Long-term debt (4) — 1,395 561 1,956 Total liabilities measured at fair value on a recurring basis 2,915 11,552 604 15,071 September 30, 2018 Level 1 Level 2 Level 3 Assets/ (in billions of yen) Assets: Trading securities (1) Japanese government bonds 1,935 32 — 1,967 Japanese local government bonds — 93 — 93 U.S. Treasury bonds and federal agency securities 2,664 193 — 2,857 Other foreign government bonds 1,705 492 — 2,197 Agency mortgage-backed securities — 1,865 — 1,865 Residential mortgage-backed securities — — 12 12 Certificates of deposit and commercial paper — 1,322 — 1,322 Corporate bonds and other 31 2,198 1,105 3,334 Equity securities 1,724 — 29 1,753 Trading securities measured at net asset value (2) 661 Derivative financial instruments: Interest rate contracts 40 4,530 37 4,607 Foreign exchange contracts 16 2,323 28 2,367 Equity-related contracts 77 220 18 315 Credit-related contracts — 20 2 22 Other contracts 12 8 29 49 Available-for-sale Japanese government bonds 12,444 1,007 — 13,451 Japanese local government bonds — 240 — 240 U.S. Treasury bonds and federal agency securities 1,134 — — 1,134 Other foreign government bonds 451 792 — 1,243 Agency mortgage-backed securities — 871 — 871 Residential mortgage-backed securities — 63 46 109 Commercial mortgage-backed securities — — 469 469 Japanese corporate bonds and other debt securities — 1,883 156 2,039 Foreign corporate bonds and other debt securities — 770 145 915 Equity securities (3) Equity securities with readily determinable fair values 4,413 90 — 4,503 Equity securities measured at net asset value (2) 35 Other investments — — 41 41 Total assets measured at fair value on a recurring basis 26,646 19,012 2,117 48,471 Liabilities: Trading securities sold, not yet purchased 2,538 268 2 2,808 Derivative financial instruments: Interest rate contracts 38 4,468 14 4,520 Foreign exchange contracts 16 2,115 3 2,134 Equity-related contracts 107 103 4 214 Credit-related contracts — 20 2 22 Other contracts 7 10 29 46 Long-term debt (4) — 1,768 612 2,380 Total liabilities measured at fair value on a recurring basis 2,706 8,752 666 12,124 Notes: (1) Trading securities include foreign currency denominated securities for which the MHFG Group elected the fair value option. (2) In accordance with ASC 820, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented for these classes of assets are intended to permit the reconciliation of the fair value hierarchy to the amounts presented in the statements of financial position. The amounts of unfunded commitments related to these investments at March 31, 2018 and September 30, 2018 were ¥31 billion and ¥40 billion, respectively. (3) The MHFG Group adopted ASU No.2016-01 on April 1, 2018. In connection with the adoption, equity securities are no longer classified as available-for-sale securities. See Note 2 “Recently issued accounting pronouncements” for further details. (4) Amounts represent items for which the Group elected the fair value option or for which it applied the practicability exception.
Reconciliation for All Assets and Liabilities 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 six months ended September 30, 2017 and 2018: Six months ended September 30, 2017 April 1, Gains Gains Transfers Transfers Purchases Sales Issuances Settle- September 30, Change in (losses) (6) (in billions of yen) Assets: Trading securities: Residential mortgage-backed securities 15 — (2) — — — — — — (1 ) 14 — Corporate bonds and other 1,052 18 (2) — 123 (240 ) 562 (276 ) — (153 ) 1,086 20 Equity securities 23 (1 ) (2) — — — — — — — 22 (1 ) Derivative financial instruments, net (1) Interest rate contracts 26 (6 ) (2) — — — — — — 1 21 (6 ) Foreign exchange contracts 8 (2 ) (2) — — — — — — — 6 (2 ) Equity-related contracts (25 ) (7 ) (2) — — — — — — 6 (26 ) (8 ) Other contracts — — (2) — — — — — — 1 1 — Available-for-sale Residential mortgage-backed securities 77 — (3) — (4) — — 1 — — (10 ) 68 — Commercial mortgage-backed securities 224 — (3) — (4) — — 40 (7 ) — — 257 — Japanese corporate bonds and other debt securities 174 (1 ) (3) (3 ) (4) — — 11 — — (16 ) 165 (1 ) Foreign corporate bonds and other debt securities 110 — (3) 1 (4) 15 (29 ) — — — — 97 — Other investments 37 — (3) — — — 12 — — (10 ) 39 — Liabilities: Trading securities sold, not yet purchased — — (2) — — — (57 ) 61 — — 4 — Long-term debt 593 (13 ) (5) — 1 (10 ) — — 47 (81 ) 563 (14 ) Six months ended September 30, 2018 April 1, Gains Gains Transfers Transfers Purchases Sales Issuances Settle- September 30, Change in (losses) (6) (in billions of yen) Assets: Trading securities: Residential mortgage-backed securities 12 — (2) — — — — — — — 12 — Corporate bonds and other 1,013 31 (2) — — — 457 (242 ) — (154 ) 1,105 35 Equity securities 23 2 (2) — — — 5 (1 ) — — 29 — Derivative financial instruments, net (1) Interest rate contracts 21 1 (2) — — — — — — 1 23 2 Foreign exchange contracts 12 15 (2) — — — — — — (2 ) 25 17 Equity-related contracts 4 (4 ) (2) — — — — — — 14 14 — Credit-related contracts 1 (3 ) (2) — — — — — — 2 — — Available-for-sale Residential mortgage-backed securities 54 — (3) — (4) — — — — — (8 ) 46 — Commercial mortgage-backed securities 441 — (3) — (4) — — 57 (28 ) — (1 ) 469 — Japanese corporate bonds and other debt securities 163 10 (3) (8 ) (4) — — 7 (7 ) — (9 ) 156 10 Foreign corporate bonds and other debt securities 80 — (3) — (4) 61 — 4 — — — 145 — Other investments 38 1 (3) — — — 13 — — (11 ) 41 2 Liabilities: Trading securities sold, not yet purchased 4 1 (2) — — — (30 ) 29 — — 2 — Long-term debt 561 2 (5) 3 (4) 2 — — — 85 (31 ) 612 4 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 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 were attributable to the change in fair value relating to assets and liabilities classified as Level 3 that were still held at September 30, 2017 and 2018.
Quantitative Information about Significant Unobservable Inputs Related to Material Classes of Level 3 Assets and Liabilities	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, 2018 and September 30, 2018: March 31, 2018 Products/Instruments Fair value Principal valuation technique Unobservable inputs Range of input values Weighted average (5) (in billions of yen, except for percentages and basis points) Trading securities and Available-for-sale Residential mortgage-backed securities 66 Discounted cash flow Price-based Prepayment rate Default rate Recovery rate Discount margin 3% - 17% 0% - 1% 100% - 100% 17bps - 170bps 7% Commercial mortgage-backed securities 441 Discounted cash flow Price-based Discount margin 9bps - 141bps 28bps Corporate bonds and other debt securities 1,256 Discounted cash flow Price-based Prepayment rate (1) Default rate (1) Recovery rate (1) Discount margin (1) Discount margin (2) 26% - 37% 1% - 2% 60% - 69% 12bps - 1,165bps 36% Derivative financial instruments, net: Interest rate contracts 21 Internal valuation model (3) IR – IR correlation Default rate (4) 23% - 100% 0% - 63% Foreign exchange contracts 12 Internal valuation model (3) FX – IR correlation FX – FX correlation Default rate (4) 16% - 53% 61% - 61% 0% - 63% Equity-related contracts 4 Internal valuation model (3) Equity – IR correlation Equity volatility 25% - 25% 12% - 41% Credit-related contracts 1 Internal valuation model (3) Default rate Credit correlation 0% - 3% 27% - 100% Long-term debt 561 Internal valuation model (3) IR – IR correlation FX – IR correlation FX – FX correlation Equity – IR correlation Equity – FX correlation Equity correlation Equity volatility Default rate Credit correlation 23% - 100% 9% - 53% 61% - 61% 25% - 25% 55% - 70% 24% - 100% 0% - 2% 28% - 100% September 30, 2018 Products/Instruments Fair value Principal valuation technique Unobservable inputs Range of input values Weighted average (5) (in billions of yen, except for percentages and basis points) Trading securities and Available-for-sale Residential mortgage-backed securities 58 Discounted cash flow Price-based Prepayment rate Default rate Recovery rate Discount margin 4% - 18% 0% - 1% 100% - 100% 15bps - 170bps 7% Commercial mortgage-backed securities 469 Discounted cash flow Price-based Discount margin 9bps - 198bps 24bps Corporate bonds and other debt securities 1,406 Discounted cash flow Price-based Prepayment rate (1) Default rate (1) Recovery rate (1) Discount margin (1) Discount margin (2) 27% - 27% 2% - 2% 69% - 69% 93bps - 1,194bps 27% Derivative financial instruments, net: Interest rate contracts 23 Internal valuation model (3) IR – IR correlation Default rate (4) 23% - 100% Foreign exchange contracts 25 Internal valuation model (3) FX – IR correlation FX – FX correlation Default rate (4) 5% - 55% 64% - 64% 0% - 63% Equity-related contracts 14 Internal valuation model (3) Equity – IR correlation Equity correlation Equity volatility 25% - 25% Credit-related contracts — Internal valuation model (3) Default rate Credit correlation 0% - 4% 28% - 100% Long-term debt 612 Internal valuation model (3) IR – IR correlation FX – IR correlation FX – FX correlation Equity – IR correlation Equity – FX correlation Equity correlation Equity volatility Default rate Credit correlation 23% - 100% 64% - 64% 0% - 4% 24% - 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 analyses. (5) Weighted averages are calculated by weighting each input by the relative fair value of the respective financial instruments.
Summary of Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis	The following table shows the fair value hierarchy for these items as of March 31, 2018 and September 30, 2018: March 31, 2018 Total Level 1 Level 2 Level 3 Aggregate cost (in billions of yen) Assets: Loans 113 — — 113 164 Loans held-for-sale 60 — 60 — 74 Equity securities (without readily determinable fair values) 1 — — 1 3 Premises and equipment—net — — — — 4 Total assets measured at fair value on a nonrecurring basis 174 — 60 114 245 September 30, 2018 Total Level 1 Level 2 Level 3 Aggregate cost (in billions of yen) Assets: Loans 113 — — 113 162 Equity securities (without readily determinable fair values) 3 — — 3 2 Other investments 5 5 — — 7 Premises and equipment—net — — — — 2 Total assets measured at fair value on a nonrecurring basis 121 5 — 116 173 Note: The fair values may not be current as of the dates indicated, but rather as of the date the fair value change occurred. Accordingly, the carrying values may not equal current fair value.
Carrying Amounts and Fair Values of Certain Financial Instruments, Excluding Financial Instruments Carried at Fair Value on a Recurring Basis and Those outside Scope of ASC 825	The following table shows the carrying amounts and fair values at March 31, 2018 and September 30, 2018, 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 equity method investments as defined in ASC 323, “Investments—Equity Method and Joint Ventures” (“ASC 323”) and lease contracts as defined in ASC 840, “Leases” (“ASC 840”): March 31, 2018 Carrying Estimated fair value Total Level 1 Level 2 Level 3 (in billions of yen) Financial assets: 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 61,381 61,381 1,206 60,175 — Investments 2,518 2,522 1,984 538 — Loans, net of allowance for loan losses (Note) 83,088 84,041 — — 84,041 Financial liabilities: Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions 43,921 43,921 22,898 21,023 — Interest-bearing deposits 113,558 113,540 61,719 51,821 — Due to trust accounts 3,993 3,993 — 3,993 — Other short-term borrowings 1,688 1,688 — 1,688 — Long-term debt 10,970 10,995 — 10,098 897 September 30, 2018 Carrying Estimated fair value Total Level 1 Level 2 Level 3 (in billions of yen) Financial assets: 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 60,425 60,425 1,128 59,297 — Investments 2,137 2,132 1,619 513 — Loans, net of allowance for loan losses (Note) 84,443 85,403 — — 85,403 Financial liabilities: Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions 50,184 50,184 24,384 25,800 — Interest-bearing deposits 108,932 108,909 55,443 53,466 — Due to trust accounts 3,966 3,966 — 3,966 — Other short-term borrowings 1,754 1,754 — 1,754 — Long-term debt 11,151 11,132 — 10,264 868 Note: Loans, net of allowance for loan losses include items measured at fair value on a nonrecurring basis.

Offsetting of financial asset_2

Offsetting of financial assets and financial liabilities (Tables)	6 Months Ended
	Sep. 30, 2018
Information of Offsetting of Financial Assets and Financial Liabilities	The following table provides information about the offsetting of financial assets and financial liabilities at March 31, 2018 and September 30, 2018. The table includes 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 recognized Gross amounts offset on the balance sheet Net amounts presented on the balance sheet (2) Financial instruments (4) Cash collateral Net (in billions of yen) March 31, 2018 Assets (1) Derivatives 9,341 — 9,341 (7,751 ) (520 ) 1,070 Receivables under resale agreements 7,804 — 7,804 (7,763 ) — 41 Receivables under securities borrowing transactions 3,904 — 3,904 (3,874 ) — 30 Total 21,049 — 21,049 (19,388 ) (520 ) 1,141 Liabilities (1) Derivatives 9,013 — 9,013 (7,758 ) (884 ) 371 Payables under repurchase agreements 15,964 — 15,964 (15,847 ) — 117 Payables under securities lending transactions 1,181 — 1,181 (1,179 ) — 2 Total 26,158 — 26,158 (24,784 ) (884 ) 490 September 30, 2018 Assets (1) Derivatives 6,766 — 6,766 (5,409 ) (571 ) 786 Receivables under resale agreements 10,144 — 10,144 (10,075 ) — 69 Receivables under securities borrowing transactions 2,032 — 2,032 (2,009 ) — 23 Total 18,942 — 18,942 (17,493 ) (571 ) 878 Liabilities (1) Derivatives 6,326 — 6,326 (5,069 ) (722 ) 535 Payables under repurchase agreements 17,066 — 17,066 (17,045 ) — 21 Payables under securities lending transactions 1,359 — 1,359 (1,355 ) — 4 Total 24,751 — 24,751 (23,469 ) (722 ) 560 Notes: (1) Amounts relating to master netting arrangements or similar agreements where the MHFG Group does not have the legal right of set-off over-the-counter OTC-cleared (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.

Repurchase agreements and sec_2

Repurchase agreements and securities lending transactions accounted for as secured borrowings (Tables)	6 Months Ended
	Sep. 30, 2018
Gross Amounts of Liabilities by Remaining Contractual Maturity	The following table shows the gross amounts of liabilities associated with repurchase agreements and securities lending transactions, by remaining contractual maturity at March 31, 2018 and September 30, 2018: Overnight and Up to 30 days 31-90 days Greater than 90 days Total (in billions of yen) March 31, 2018 Repurchase agreements 255 11,669 3,676 1,057 16,657 Securities lending transactions 1,270 355 — 208 1,833 Total 1,525 12,024 3,676 1,265 18,490 September 30, 2018 Repurchase agreements 4,095 10,198 1,687 1,508 17,488 Securities lending transactions 1,068 771 — 273 2,112 Total 5,163 10,969 1,687 1,781 19,600
Gross Amounts of Liabilities by Class of Underlying Collateral	The following table shows the gross amounts of liabilities associated with repurchase agreements and securities lending transactions, by class of underlying collateral at March 31, 2018 and September 30, 2018: Repurchase Securities lending (in billions of yen) March 31, 2018 Japanese government bonds and Japanese local government bonds 1,358 592 Foreign government bonds and foreign agency mortgage-backed securities 14,426 303 Commercial paper and corporate bonds 328 48 Equity securities 406 869 Other 139 21 Total (Note) 16,657 1,833 September 30, 2018 Japanese government bonds and Japanese local government bonds 2,365 320 Foreign government bonds and foreign agency mortgage-backed securities 14,157 700 Commercial paper and corporate bonds 383 51 Equity securities 418 1,021 Other 165 20 Total (Note) 17,488 2,112 Note: Amounts exceeded the gross amounts recognized in Note 18 “Offsetting of financial assets and financial liabilities” by ¥1,345 billion and ¥1,175 billion, at March 31, 2018 and September 30, 2018, respectively, which excluded the amounts relating to master netting agreements or similar agreements where the MHFG Group did not have the legal right of set-off

Business segment information (T

Business segment information (Tables)	6 Months Ended
	Sep. 30, 2018
Reportable Segment Information Derived from Internal Management Reporting Systems, on Basis of Japanese GAAP	The reportable segment information, set forth below, is derived from the internal management reporting systems used by management to measure the performance of the Group’s operating segments. Management measures the performance of each of the operating segments in accordance with internal managerial accounting rules and practices. In addition, the format and information are presented primarily on the basis of Japanese GAAP. Therefore, they are not consistent with the consolidated financial statements prepared in accordance with U.S. GAAP. A reconciliation is provided for the total amount of each business segment’s “Net business profits (losses) + Net gains (losses) related to ETFs and others” with income before income tax expense under U.S. GAAP. Management does not use information on business segment’s assets to allocate resources and assess performance and has not prepared information on the segment’s assets. Accordingly, information on the segment’s assets is not available. MHFG (Consolidated) Six months ended September 30, 2017 (4) Retail & Corporate & Global Global Asset Others (3) Total (in billions of yen) Gross profits + Net gains (losses) related to ETFs and others (1) 343.2 187.6 153.2 239.9 24.8 32.5 981.2 General and administrative expenses 358.9 101.3 121.6 100.3 13.9 15.3 711.3 Equity in earnings (losses) of equity method investees—net 7.5 0.6 1.3 — 0.5 0.7 10.6 Amortization of goodwill and others 0.2 0.2 0.2 1.2 4.0 1.2 7.0 Others — — — — — (10.5 ) (10.5 ) Net business profits (losses) (2) (8.4 ) 86.7 32.7 138.4 7.4 6.2 263.0 MHFG (Consolidated) Six months ended September 30, 2018 (4) Retail & Corporate & Global Global Asset Others (3) Total (in billions of yen) Gross profits + Net gains (losses) related to ETFs and others (1) 345.9 223.7 198.2 237.4 25.0 21.3 1,051.5 General and administrative expenses 360.2 100.3 121.4 103.5 13.9 23.4 722.7 Equity in earnings (losses) of equity method investees—net 14.4 0.6 2.8 — 0.6 1.0 19.4 Amortization of goodwill and others 0.2 0.2 0.2 1.2 4.0 1.0 6.8 Others — — — — — (10.4 ) (10.4 ) Net business profits (losses) (2) (0.1 ) 123.8 79.4 132.7 7.7 (12.5 ) 331.0 Notes: (1) “Gross profits + Net gains (losses) related to ETFs and others” is reported instead of sales reported by general corporations. Gross profits is defined as the sum of net interest income, fiduciary income, net fee and commission income, net trading income and net other operating income. Net gains (losses) related to ETFs and others consist of net gains (losses) on ETFs held by MHBK and MHTB and net gains (losses) on operating investment securities of MHSC on its consolidated basis. For the six months ended September 30, 2017 and 2018, net gains related to ETFs and others amounted to ¥21.4 billion and ¥39.9 billion, respectively, of which ¥13.9 billion and ¥33.6 billion, respectively, are included in “Global Markets Company”. (2) Net business profits is used in Japan as a measure of the profitability of core banking operations. Measurement of net business profits is required for regulatory reporting to the Financial Services Agency. (3) “Others” includes items which should be eliminated as internal transactions between each segment on a consolidated basis. (4) Beginning on April 1, 2018, new allocation methods for transactions between each segment and “Others” have been applied. In connection with the use of the new allocation methods, the presentation of “Net business profits” has changed to “Net business profits (losses) + Net gains (losses) related to ETFs and others”. Before the change, “Net gains (losses) related to ETFs and others” were included in “Gross profits” of each segment and eliminated in “Others”. In addition, “Amortization of goodwill and others” has been presented as a new item. Figures for the six months ended September 30, 2017 have been restated for the new allocation methods. These changes more appropriately reflect the performance of each of the operating segments in accordance with internal managerial accounting rules and practices. Furthermore, income and expenses of foreign branches of MHBK and foreign subsidiaries with functional currency other than Japanese Yen have been translated for purpose of segment reporting using the budgeted foreign currency rates. Prior period comparative amounts for these foreign currency adjustments have been translated using current period budgeted foreign currency rates.
Reconciliation of Total Net Business Profits under Internal Management Reporting Systems to Income Before Income Tax Expense on Consolidated Statements of Income	A reconciliation of “Net business profits (losses) + Net gains (losses) related to ETFs and others” under the internal management reporting systems for the six months ended September 30, 2017 and 2018 presented above to income before income tax expense shown on the consolidated statements of income is as follows: Six months ended September 30, 2017 2018 (in billions of yen) Net business profits (losses) + Net gains (losses) related to ETFs and others 263.0 331.0 Less: Net gains (losses) related to ETFs and others (21.4 ) (39.9 ) U.S. GAAP adjustments 95.7 (160.0 ) (Provision) credit for loan losses 118.0 13.3 Net gains (losses) related to equity investments 100.9 289.5 Non-recurring (3.6 ) 0.9 Gains on disposal of premises and equipment 4.6 4.3 (Provision) credit for losses on off-balance-sheet 4.2 9.9 Others—net (48.5 ) (31.4 ) Income before income tax expense 512.9 417.6

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Significant Accounting Policies [Line Items]
Decrease in Net cash provided by (used in) operating activities	¥ (1,900,047)	¥ (2,524,932)
Increase in Net cash provided by (used in) investing activities	121,329	(393,426)
Total assets	204,178,804		¥ 204,255,642
Trust and Custody Services Bank Ltd [Member]
Significant Accounting Policies [Line Items]
Total assets	¥ 9,000,000
Accounting Standards Update 2016-18 [Member]
Significant Accounting Policies [Line Items]
Decrease in Net cash provided by (used in) operating activities		(3,415)
Increase in Net cash provided by (used in) investing activities		¥ 3,932,027

Recently Issued Accounting Pr_2

Recently Issued Accounting Pronouncements - Additional Information (Detail) - JPY (¥) ¥ in Millions	Apr. 01, 2018	Mar. 31, 2018
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principles, net of tax		¥ 1,537,322
Accumulated Other Comprehensive Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principles, net of tax		(1,535,142)
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease payments		¥ 246,000
ASU No.2016-01 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principles, net of tax	¥ 1,542,000
ASU No.2016-01 | Retained Earnings | Equity Method Investments [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principles, net of tax	1,527,000
ASU No.2016-01 | Accumulated Other Comprehensive Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principles, net of tax	¥ 10,000

Investments (Amortized Cost, Gr

Investments (Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Available-for-Sale and Held-to-Maturity Securities) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities		¥ 20,461,313	¥ 21,181,709
Gross unrealized gains, available-for-sale securities		53,601	2,521,529
Gross unrealized losses, available-for-sale securities		43,299	37,610
Fair value, available-for-sale securities		20,471,615	23,665,628
Amortized cost, held-to-maturity securities		2,137,011	2,517,551
Gross unrealized gains, held-to-maturity securities		19,418	24,472
Gross unrealized losses, held-to-maturity securities		24,153	20,177
Total		2,132,276	2,521,846
Debt securities | Japanese government bonds
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities		13,468,933	13,334,619
Gross unrealized gains, available-for-sale securities		3,947	7,332
Gross unrealized losses, available-for-sale securities		21,693	9,656
Fair value, available-for-sale securities		13,451,187	13,332,295
Amortized cost, held-to-maturity securities		1,599,900	1,959,910
Gross unrealized gains, held-to-maturity securities		19,418	24,472
Total		1,619,318	1,984,382
Debt securities | Japanese local government bonds
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities		240,193	236,711
Gross unrealized gains, available-for-sale securities		914	2,903
Gross unrealized losses, available-for-sale securities		652	280
Fair value, available-for-sale securities		240,455	239,334
Debt securities | U.S. Treasury bonds and federal agency securities
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities		1,138,917	689,297
Gross unrealized gains, available-for-sale securities		78	109
Gross unrealized losses, available-for-sale securities		5,204	3,557
Fair value, available-for-sale securities		1,133,791	685,849
Debt securities | Foreign corporate bonds and other debt securities
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities	[1]	913,328	879,506
Gross unrealized gains, available-for-sale securities	[1]	2,580	1,927
Gross unrealized losses, available-for-sale securities	[1]	985	2,082
Fair value, available-for-sale securities	[1]	914,923	879,351
Debt securities | Agency mortgage-backed securities
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities	[2]	871,031	882,686
Gross unrealized gains, available-for-sale securities	[2]	9,984	13,356
Gross unrealized losses, available-for-sale securities	[2],[3]	10,008	7,628
Fair value, available-for-sale securities	[2]	871,007	888,414
Amortized cost, held-to-maturity securities	[4]	537,111	557,641
Gross unrealized losses, held-to-maturity securities	[4]	24,153	20,177
Total	[4]	512,958	537,464
Debt securities | Residential mortgage-backed securities
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities		108,963	117,870
Gross unrealized gains, available-for-sale securities		908	1,264
Gross unrealized losses, available-for-sale securities		434	281
Fair value, available-for-sale securities		109,437	118,853
Debt securities | Commercial mortgage-backed securities
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities		465,251	437,115
Gross unrealized gains, available-for-sale securities		3,641	4,132
Gross unrealized losses, available-for-sale securities		298	323
Fair value, available-for-sale securities		468,594	440,924
Debt securities | Japanese corporate bonds and other debt securities
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities	[5]	2,010,207	1,950,947
Gross unrealized gains, available-for-sale securities	[5]	30,992	40,290
Gross unrealized losses, available-for-sale securities	[5]	2,356	1,410
Fair value, available-for-sale securities	[5]	2,038,843	1,989,827
Debt securities | Other foreign government bonds
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities		1,244,490	1,057,852
Gross unrealized gains, available-for-sale securities		557	1,043
Gross unrealized losses, available-for-sale securities		1,669	1,102
Fair value, available-for-sale securities		¥ 1,243,378	1,057,793
Equity securities (marketable)
Schedule of Investments [Line Items]
Amortized cost, available-for-sale securities	[6]		1,595,106
Gross unrealized gains, available-for-sale securities	[6]		2,449,173
Gross unrealized losses, available-for-sale securities	[6]		11,291
Fair value, available-for-sale securities	[6]		¥ 4,032,988
[1]	Other debt securities presented in this line primarily consist of Foreign NCDs and asset-backed securities ("ABS"), of which the total fair values were ¥313,164 million at March 31, 2018, and ¥342,999 million at September 30, 2018.
[2]	Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥742,565 million and ¥145,849 million, respectively, at March 31, 2018, and ¥728,836 million and ¥142,171 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Government National Mortgage Association ("Ginnie Mae") securities, which are guaranteed by the United States government.
[3]	Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥88,017 million and ¥145,743 million, respectively, at March 31, 2018, and ¥214,480 million and ¥142,089 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Ginnie Mae securities, which are guaranteed by the United States government.
[4]	All Agency mortgage-backed securities presented in this line are Ginnie Mae securities.
[5]	Other debt securities presented in this line primarily consist of Japanese negotiable certificates of deposit ("NCDs"), of which the total fair values were ¥106,101 million at March 31, 2018, and ¥104,775 million at September 30, 2018.
[6]	The MHFG Group adopted ASU No.2016-01 on April 1, 2018, resulting in a cumulative-effect adjustment from AOCI to Retained earnings for net unrealized gains on equity securities (marketable). The available-for-sale category was eliminated for equity securities effective April 1, 2018. See Note 2 "Recently issued accounting pronouncements" for further details.

Investments (Amortized Cost, _2

Investments (Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Available-for-Sale and Held-to-Maturity Securities) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Schedule of Investments [Line Items]
Fair value, available-for-sale securities		¥ 20,471,615	¥ 23,665,628
Debt securities | Agency mortgage-backed securities
Schedule of Investments [Line Items]
Fair value, available-for-sale securities	[1]	871,007	888,414
Debt securities | Foreign agency mortgage-backed securities | Agency mortgage-backed securities
Schedule of Investments [Line Items]
Fair value, available-for-sale securities		728,836	742,565
Debt securities | Japanese agency mortgage-backed securities | Agency mortgage-backed securities
Schedule of Investments [Line Items]
Fair value, available-for-sale securities		142,171	145,849
Japanese government and corporate debt securities | Negotiable Certificates of Deposits and Asset- Backed Securities
Schedule of Investments [Line Items]
Fair value, available-for-sale securities		104,775	106,101
Foreign government and corporate debt securities | Negotiable certificates of deposits, asset- backed securities and collateral loan obligations
Schedule of Investments [Line Items]
Fair value, available-for-sale securities		¥ 342,999	¥ 313,164
[1]	Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥742,565 million and ¥145,849 million, respectively, at March 31, 2018, and ¥728,836 million and ¥142,171 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Government National Mortgage Association ("Ginnie Mae") securities, which are guaranteed by the United States government.

Investments (Amortized Cost and

Investments (Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities by Contractual Maturity) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Investments Classified by Contractual Maturity Date [Line Items]
Due in one year or less, amortized cost		¥ 11,331,440
Due after one year through five years, amortized cost		5,623,764
Due after five years through ten years,amortized cost		1,948,667
Due after ten years, amortized cost		1,557,442
Total		20,461,313
Due in one year or less, amortized cost		960,044
Due after one year through five years, amortized cost		479,868
Due after five years through ten years, amortized cost		159,988
Due after ten years, amortized cost		537,111
Amortized cost, held-to-maturity securities		2,137,011	¥ 2,517,551
Due in one year or less, fair value		11,353,502
Due after one year through five years, fair value		5,627,607
Due after five years through ten years, fair value		1,937,203
Due after ten years, fair value		1,553,303
Total		20,471,615
Due in one year or less, fair value		961,712
Due after one year through five years, fair value		492,560
Due after five years through ten years, fair value		165,046
Due after ten years, fair value		512,958
Total		2,132,276	2,521,846
Debt securities | Japanese government bonds
Investments Classified by Contractual Maturity Date [Line Items]
Due in one year or less, amortized cost		8,373,572
Due after one year through five years, amortized cost		3,722,338
Due after five years through ten years,amortized cost		1,063,748
Due after ten years, amortized cost		309,275
Total		13,468,933
Due in one year or less, amortized cost		960,044
Due after one year through five years, amortized cost		479,868
Due after five years through ten years, amortized cost		159,988
Amortized cost, held-to-maturity securities		1,599,900	1,959,910
Due in one year or less, fair value		8,372,894
Due after one year through five years, fair value		3,722,825
Due after five years through ten years, fair value		1,054,008
Due after ten years, fair value		301,460
Total		13,451,187
Due in one year or less, fair value		961,712
Due after one year through five years, fair value		492,560
Due after five years through ten years, fair value		165,046
Total		1,619,318	1,984,382
Debt securities | Japanese local government bonds
Investments Classified by Contractual Maturity Date [Line Items]
Due in one year or less, amortized cost		29,530
Due after one year through five years, amortized cost		143,921
Due after five years through ten years,amortized cost		61,579
Due after ten years, amortized cost		5,163
Total		240,193
Due in one year or less, fair value		29,558
Due after one year through five years, fair value		144,269
Due after five years through ten years, fair value		61,492
Due after ten years, fair value		5,136
Total		240,455
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		1,033,650
Due after five years through ten years,amortized cost		105,267
Total		1,138,917
Due in one year or less, fair value		1,033,135
Due after five years through ten years, fair value		100,656
Total		1,133,791
Debt securities | Other foreign government bonds
Investments Classified by Contractual Maturity Date [Line Items]
Due in one year or less, amortized cost		970,819
Due after one year through five years, amortized cost		258,152
Due after five years through ten years,amortized cost		12,602
Due after ten years, amortized cost		2,917
Total		1,244,490
Due in one year or less, fair value		970,233
Due after one year through five years, fair value		257,751
Due after five years through ten years, fair value		12,489
Due after ten years, fair value		2,905
Total		1,243,378
Debt securities | Agency mortgage-backed securities
Investments Classified by Contractual Maturity Date [Line Items]
Due after ten years, amortized cost		871,031
Total		871,031
Due after ten years, amortized cost		537,111
Amortized cost, held-to-maturity securities	[1]	537,111	557,641
Due after ten years, fair value		871,007
Total		871,007
Due after ten years, fair value		512,958
Total	[1]	512,958	¥ 537,464
Debt securities | Residential mortgage-backed securities
Investments Classified by Contractual Maturity Date [Line Items]
Due after ten years, amortized cost		108,963
Total		108,963
Due after ten years, fair value		109,437
Total		109,437
Debt securities | Commercial mortgage-backed securities
Investments Classified by Contractual Maturity Date [Line Items]
Due in one year or less, amortized cost		1,852
Due after one year through five years, amortized cost		178,690
Due after five years through ten years,amortized cost		212,459
Due after ten years, amortized cost		72,250
Total		465,251
Due in one year or less, fair value		1,852
Due after one year through five years, fair value		179,517
Due after five years through ten years, fair value		214,475
Due after ten years, fair value		72,750
Total		468,594
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		407,643
Due after one year through five years, amortized cost		989,938
Due after five years through ten years,amortized cost		427,553
Due after ten years, amortized cost		185,073
Total		2,010,207
Due in one year or less, fair value		431,664
Due after one year through five years, fair value		991,020
Due after five years through ten years, fair value		428,321
Due after ten years, fair value		187,838
Total		2,038,843
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		514,374
Due after one year through five years, amortized cost		330,725
Due after five years through ten years,amortized cost		65,459
Due after ten years, amortized cost		2,770
Total		913,328
Due in one year or less, fair value		514,166
Due after one year through five years, fair value		332,225
Due after five years through ten years, fair value		65,762
Due after ten years, fair value		2,770
Total		¥ 914,923
[1]	All Agency mortgage-backed securities presented in this line are Ginnie Mae securities.

Investments - Additional Inform

Investments - Additional Information (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Gain (Loss) on Securities [Line Items]
Equity method Investments, carrying value	¥ 301,524		¥ 280,666
Held-to-maturity Securities
Gain (Loss) on Securities [Line Items]
Impairment loss on securities	¥ 0	¥ 0
Orient Corporation
Gain (Loss) on Securities [Line Items]
Percentage of proportionate share to the total outstanding common stock	49.00%
Equity securities (marketable)
Gain (Loss) on Securities [Line Items]
Equity method Investments, carrying value	¥ 167,316		152,445
Equity method Investments, aggregated market values	¥ 312,520		¥ 324,239

Investments (Other-Than-Tempora

Investments (Other-Than-Temporary Impairment Losses on Available-for-Sale Securities) (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Gain (Loss) on Securities [Line Items]
Other-than-temporary impairment on available-for-sale securities	¥ 213	¥ 3,521
Debt securities
Gain (Loss) on Securities [Line Items]
Other-than-temporary impairment on available-for-sale securities	¥ 213	1,000
Equity securities
Gain (Loss) on Securities [Line Items]
Other-than-temporary impairment on available-for-sale securities		¥ 2,521

Investments (Gross Unrealized L

Investments (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 a Continuous Unrealized Loss Position) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities		¥ 9,463,724	¥ 10,402,277
Less than 12 months Gross unrealized losses, available-for-sale securities		20,475	22,884
12 months or more Fair value, available-for-sale securities		4,400,160	3,698,632
12 months or more Gross unrealized losses, available-for-sale securities		22,824	14,726
Total Fair value, available-for-sale securities		13,863,884	14,100,909
Total Gross unrealized losses, available-for-sale securities		43,299	37,610
Less than 12 months, Fair value, held-to-maturity securities		22,319	30,589
Less than 12 months Gross unrealized losses, held-to-maturity securities		827	766
12 months or more Fair value, held-to-maturity securities		490,639	506,875
12 months or more Gross unrealized losses, held-to-maturity securities		23,326	19,411
Total Fair value, held-to-maturity securities		512,958	537,464
Total Gross unrealized losses, held-to-maturity securities		24,153	20,177
Debt securities | Japanese government bonds
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities		6,763,194	8,052,820
Less than 12 months Gross unrealized losses, available-for-sale securities		13,798	3,716
12 months or more Fair value, available-for-sale securities		3,243,600	2,868,078
12 months or more Gross unrealized losses, available-for-sale securities		7,895	5,940
Total Fair value, available-for-sale securities		10,006,794	10,920,898
Total Gross unrealized losses, available-for-sale securities		21,693	9,656
Debt securities | Japanese local government bonds
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities		92,616	28,827
Less than 12 months Gross unrealized losses, available-for-sale securities		329	139
12 months or more Fair value, available-for-sale securities		83,400	58,998
12 months or more Gross unrealized losses, available-for-sale securities		323	141
Total Fair value, available-for-sale securities		176,016	87,825
Total Gross unrealized losses, available-for-sale securities		652	280
Debt securities | U.S. Treasury bonds and federal agency securities
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities		961,157	515,005
Less than 12 months Gross unrealized losses, available-for-sale securities		2,107	3,557
12 months or more Fair value, available-for-sale securities		52,378
12 months or more Gross unrealized losses, available-for-sale securities		3,097
Total Fair value, available-for-sale securities		1,013,535	515,005
Total Gross unrealized losses, available-for-sale securities		5,204	3,557
Debt securities | Other foreign government bonds
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities		704,626	419,648
Less than 12 months Gross unrealized losses, available-for-sale securities		1,023	1,030
12 months or more Fair value, available-for-sale securities		46,274	68,359
12 months or more Gross unrealized losses, available-for-sale securities		646	72
Total Fair value, available-for-sale securities		750,900	488,007
Total Gross unrealized losses, available-for-sale securities		1,669	1,102
Debt securities | Agency mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities	[1]	151,610	45,434
Less than 12 months Gross unrealized losses, available-for-sale securities	[1]	782	1,116
12 months or more Fair value, available-for-sale securities	[1]	204,959	188,326
12 months or more Gross unrealized losses, available-for-sale securities	[1]	9,226	6,512
Total Fair value, available-for-sale securities	[1]	356,569	233,760
Total Gross unrealized losses, available-for-sale securities	[1],[2]	10,008	7,628
Less than 12 months, Fair value, held-to-maturity securities	[3]	22,319	30,589
Less than 12 months Gross unrealized losses, held-to-maturity securities	[3]	827	766
12 months or more Fair value, held-to-maturity securities	[3]	490,639	506,875
12 months or more Gross unrealized losses, held-to-maturity securities	[3]	23,326	19,411
Total Fair value, held-to-maturity securities	[3]	512,958	537,464
Total Gross unrealized losses, held-to-maturity securities	[3]	24,153	20,177
Debt securities | Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities		26,351	11,336
Less than 12 months Gross unrealized losses, available-for-sale securities		151	14
12 months or more Fair value, available-for-sale securities		24,883	16,129
12 months or more Gross unrealized losses, available-for-sale securities		283	267
Total Fair value, available-for-sale securities		51,234	27,465
Total Gross unrealized losses, available-for-sale securities		434	281
Debt securities | Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities		44,603	68,723
Less than 12 months Gross unrealized losses, available-for-sale securities		118	242
12 months or more Fair value, available-for-sale securities		42,526	7,835
12 months or more Gross unrealized losses, available-for-sale securities		180	81
Total Fair value, available-for-sale securities		87,129	76,558
Total Gross unrealized losses, available-for-sale securities		298	323
Debt securities | Japanese corporate bonds and other debt securities
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities		497,300	563,831
Less than 12 months Gross unrealized losses, available-for-sale securities		1,767	933
12 months or more Fair value, available-for-sale securities		599,554	403,069
12 months or more Gross unrealized losses, available-for-sale securities		589	477
Total Fair value, available-for-sale securities		1,096,854	966,900
Total Gross unrealized losses, available-for-sale securities	[4]	2,356	1,410
Debt securities | Foreign corporate bonds and other debt securities
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities		222,267	358,410
Less than 12 months Gross unrealized losses, available-for-sale securities		400	888
12 months or more Fair value, available-for-sale securities		102,586	87,472
12 months or more Gross unrealized losses, available-for-sale securities		585	1,194
Total Fair value, available-for-sale securities		324,853	445,882
Total Gross unrealized losses, available-for-sale securities	[5]	¥ 985	2,082
Equity securities (marketable)
Gain (Loss) on Securities [Line Items]
Less than 12 months, Fair value, available-for-sale securities			338,243
Less than 12 months Gross unrealized losses, available-for-sale securities			11,249
12 months or more Fair value, available-for-sale securities			366
12 months or more Gross unrealized losses, available-for-sale securities			42
Total Fair value, available-for-sale securities			338,609
Total Gross unrealized losses, available-for-sale securities	[6]		¥ 11,291
[1]	Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥88,017 million and ¥145,743 million, respectively, at March 31, 2018, and ¥214,480 million and ¥142,089 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Ginnie Mae securities, which are guaranteed by the United States government.
[2]	Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥742,565 million and ¥145,849 million, respectively, at March 31, 2018, and ¥728,836 million and ¥142,171 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Government National Mortgage Association ("Ginnie Mae") securities, which are guaranteed by the United States government.
[3]	All Agency mortgage-backed securities presented in this line are Ginnie Mae securities.
[4]	Other debt securities presented in this line primarily consist of Japanese negotiable certificates of deposit ("NCDs"), of which the total fair values were ¥106,101 million at March 31, 2018, and ¥104,775 million at September 30, 2018.
[5]	Other debt securities presented in this line primarily consist of Foreign NCDs and asset-backed securities ("ABS"), of which the total fair values were ¥313,164 million at March 31, 2018, and ¥342,999 million at September 30, 2018.
[6]	The MHFG Group adopted ASU No.2016-01 on April 1, 2018, resulting in a cumulative-effect adjustment from AOCI to Retained earnings for net unrealized gains on equity securities (marketable). The available-for-sale category was eliminated for equity securities effective April 1, 2018. See Note 2 "Recently issued accounting pronouncements" for further details.

Investments (Gross Unrealized_2

Investments (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 a Continuous Unrealized Loss Position) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Gain (Loss) on Securities [Line Items]
Fair value, available-for-sale securities		¥ 13,863,884	¥ 14,100,909
Debt securities | Agency mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Fair value, available-for-sale securities	[1]	356,569	233,760
Debt securities | Japanese agency mortgage-backed securities | Agency mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Fair value, available-for-sale securities		214,480	88,017
Debt securities | Foreign agency mortgage-backed securities | Agency mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Fair value, available-for-sale securities		¥ 142,089	¥ 145,743
[1]	Agency mortgage-backed securities presented in this line consist of Japanese and Foreign agency mortgage-backed securities, of which the fair values were ¥88,017 million and ¥145,743 million, respectively, at March 31, 2018, and ¥214,480 million and ¥142,089 million, respectively, at September 30, 2018. All Japanese agency mortgage-backed securities are issued by Japan Housing Finance Agency, a Japanese government-sponsored enterprise. Foreign agency mortgage-backed securities primarily consist of Ginnie Mae securities, which are guaranteed by the United States government.

Investments (Realized Gains and

Investments (Realized Gains and Losses on Sales of Available-for-Sale Securities) (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Gross realized gains	¥ 9,955	¥ 127,360
Gross realized losses	(8,497)	(10,020)
Net realized gains (losses) on sales of available-for-sale securities	¥ 1,458	¥ 117,340

Investments (Summary of Composi

Investments (Summary of Composition of Other Investments) (Detail) - JPY (¥) ¥ in Millions	Sep. 30, 2018	Mar. 31, 2018
Schedule of Investments [Line Items]
Equity method investments	¥ 301,524	¥ 280,666
Investments held by consolidated investment companies	41,230	37,735
Other equity interests		267,495
Total	¥ 342,754	¥ 585,896

Investments - Summary of Detail

Investments - Summary of Details of Net Gains and Losses on Equity Securities (Detail) ¥ in Millions	6 Months Ended
	Sep. 30, 2018JPY (¥)
Gain (Loss) on Securities [Line Items]
Net gains and losses recognized during the period on equity securities	¥ 306,788
Less: Net gains and losses recognized during the period on equity securities sold during the period	116,308
Unrealized gains and losses recognized during the reporting period on equity securities still held at the reporting period	¥ 190,480

Investments - Summary of Equity

Investments - Summary of Equity Securities Without Readily Determinable Fair Values (Detail) ¥ in Millions	6 Months Ended
	Sep. 30, 2018JPY (¥)
Equity Securities without Readily Determinable Fair Value [Line Items]
Carrying amounts at the end of the period	¥ 231,810
During the period	976
Cumulative	976
During the period	1,837
Cumulative	¥ 1,837

Loans (Loans Outstanding by Dom

Loans (Loans Outstanding by Domicile and Industry of Borrower) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[1]	¥ 84,980,549	¥ 83,661,340
Less: Unearned income and deferred loan fees-net		150,301	146,696
Loans outstanding		84,830,248	83,514,644
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		56,463,093	58,660,514
Domestic | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		8,469,440	8,156,341
Domestic | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		8,475,834	8,101,668
Domestic | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		5,288,571	5,024,018
Domestic | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		5,168,408	5,112,673
Domestic | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		3,710,990	3,564,869
Domestic | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		4,455,338	4,471,423
Domestic | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		5,776,149	8,882,125
Domestic | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[2]	5,059,891	5,018,387
Domestic | Mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		9,191,280	9,445,286
Domestic | Other individual loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		867,192	883,724
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[3]	28,517,456	25,000,826
Foreign | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		8,527,586	7,465,140
Foreign | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		625,263	302,891
Foreign | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		19,322,908	17,195,159
Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		¥ 41,699	¥ 37,636
[1]	Amounts represent loan balances before deducting unearned income and deferred loan fees.
[2]	Other industries of Domestic includes trade receivables and lease receivables of consolidated VIEs.
[3]	The majority of Total foreign consist of Commercial and Industrial loans.

Loans - Additional Information

Loans - Additional Information (Detail) - JPY (¥) ¥ in Millions	6 Months Ended	12 Months Ended
	Sep. 30, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net losses on sales of loans	¥ 1,060	¥ 3,739
Loans held for sale	15,758	86,153
Impaired Financing Receivables with No Related Allowance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans partially charged off	¥ 27,759	¥ 29,037

Loans (Credit Quality Informati

Loans (Credit Quality Information of Loans Based on MHFG Group's Internal Rating System) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[1]	¥ 84,980,549	¥ 83,661,340
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		56,463,093	58,660,514
Domestic | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		8,469,440	8,156,341
Domestic | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		8,475,834	8,101,668
Domestic | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		5,288,571	5,024,018
Domestic | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		5,168,408	5,112,673
Domestic | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		3,710,990	3,564,869
Domestic | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		4,455,338	4,471,423
Domestic | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		5,776,149	8,882,125
Domestic | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[2]	5,059,891	5,018,387
Domestic | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		10,058,472	10,329,010
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[3]	28,517,456	25,000,826
Foreign | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		8,527,586	7,465,140
Foreign | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		625,263	302,891
Foreign | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		19,322,908	17,195,159
Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		41,699	37,636
Financing Receivables Not Impaired | Normal obligors | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		63,820,453	59,248,942
Financing Receivables Not Impaired | Normal obligors | Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	10,600,069	10,883,141
Financing Receivables Not Impaired | Normal obligors | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	8,801,849	11,467,703
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		38,770,143	37,803,998
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		8,130,139	7,705,495
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		7,709,697	7,317,972
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		4,731,189	4,535,793
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		4,694,532	4,636,236
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		3,558,659	3,414,781
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		4,236,485	4,244,101
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		2,594,132	3,010,708
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[2]	2,888,378	2,716,502
Financing Receivables Not Impaired | Normal obligors | Domestic | Corporate | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		226,932	222,410
Financing Receivables Not Impaired | Normal obligors | Domestic | Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	10,590,929	10,873,687
Financing Receivables Not Impaired | Normal obligors | Domestic | Retail | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	72,651	77,947
Financing Receivables Not Impaired | Normal obligors | Domestic | Retail | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	522,815	541,778
Financing Receivables Not Impaired | Normal obligors | Domestic | Retail | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	168,384	172,045
Financing Receivables Not Impaired | Normal obligors | Domestic | Retail | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	169,576	177,965
Financing Receivables Not Impaired | Normal obligors | Domestic | Retail | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	73,437	76,532
Financing Receivables Not Impaired | Normal obligors | Domestic | Retail | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	1,741	1,640
Financing Receivables Not Impaired | Normal obligors | Domestic | Retail | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[2],[4]	2,996	3,536
Financing Receivables Not Impaired | Normal obligors | Domestic | Retail | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	9,579,329	9,822,244
Financing Receivables Not Impaired | Normal obligors | Domestic | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	5,833,559	8,523,806
Financing Receivables Not Impaired | Normal obligors | Domestic | Other | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	15,714	23,343
Financing Receivables Not Impaired | Normal obligors | Domestic | Other | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	10,358	13,332
Financing Receivables Not Impaired | Normal obligors | Domestic | Other | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	206,848	141,718
Financing Receivables Not Impaired | Normal obligors | Domestic | Other | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	17,496	17,305
Financing Receivables Not Impaired | Normal obligors | Domestic | Other | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	529	1,774
Financing Receivables Not Impaired | Normal obligors | Domestic | Other | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	184,392	196,431
Financing Receivables Not Impaired | Normal obligors | Domestic | Other | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	3,182,017	5,871,417
Financing Receivables Not Impaired | Normal obligors | Domestic | Other | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[2],[5]	2,148,915	2,170,442
Financing Receivables Not Impaired | Normal obligors | Domestic | Other | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	67,290	88,044
Financing Receivables Not Impaired | Normal obligors | Foreign | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		25,050,310	21,444,944
Financing Receivables Not Impaired | Normal obligors | Foreign | Corporate | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		7,988,472	6,949,036
Financing Receivables Not Impaired | Normal obligors | Foreign | Corporate | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		623,460	301,072
Financing Receivables Not Impaired | Normal obligors | Foreign | Corporate | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		16,430,107	14,192,930
Financing Receivables Not Impaired | Normal obligors | Foreign | Corporate | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		8,271	1,906
Financing Receivables Not Impaired | Normal obligors | Foreign | Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	9,140	9,454
Financing Receivables Not Impaired | Normal obligors | Foreign | Retail | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	116	209
Financing Receivables Not Impaired | Normal obligors | Foreign | Retail | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4]	9,024	9,245
Financing Receivables Not Impaired | Normal obligors | Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	2,968,290	2,943,897
Financing Receivables Not Impaired | Normal obligors | Foreign | Other | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	515,716	487,978
Financing Receivables Not Impaired | Normal obligors | Foreign | Other | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	2,431,047	2,432,189
Financing Receivables Not Impaired | Normal obligors | Foreign | Other | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5]	21,527	23,730
Financing Receivables Not Impaired | Watch obligors | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		983,629	1,091,660
Financing Receivables Not Impaired | Watch obligors | Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	154,430	165,250
Financing Receivables Not Impaired | Watch obligors | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5],[6]	52,275	189,384
Financing Receivables Not Impaired | Watch obligors | Domestic | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		618,211	665,061
Financing Receivables Not Impaired | Watch obligors | Domestic | Corporate | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		124,530	197,465
Financing Receivables Not Impaired | Watch obligors | Domestic | Corporate | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		178,226	172,287
Financing Receivables Not Impaired | Watch obligors | Domestic | Corporate | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		91,898	95,223
Financing Receivables Not Impaired | Watch obligors | Domestic | Corporate | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		132,233	121,832
Financing Receivables Not Impaired | Watch obligors | Domestic | Corporate | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		39,194	35,339
Financing Receivables Not Impaired | Watch obligors | Domestic | Corporate | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		23,084	16,716
Financing Receivables Not Impaired | Watch obligors | Domestic | Corporate | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[2]	8,346	2,708
Financing Receivables Not Impaired | Watch obligors | Domestic | Corporate | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		20,700	23,491
Financing Receivables Not Impaired | Watch obligors | Domestic | Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	154,365	165,244
Financing Receivables Not Impaired | Watch obligors | Domestic | Retail | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	8,305	9,775
Financing Receivables Not Impaired | Watch obligors | Domestic | Retail | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	15,083	15,466
Financing Receivables Not Impaired | Watch obligors | Domestic | Retail | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	18,863	21,109
Financing Receivables Not Impaired | Watch obligors | Domestic | Retail | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	27,000	27,975
Financing Receivables Not Impaired | Watch obligors | Domestic | Retail | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	8,313	8,916
Financing Receivables Not Impaired | Watch obligors | Domestic | Retail | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	265	194
Financing Receivables Not Impaired | Watch obligors | Domestic | Retail | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[2],[4],[6]	375	259
Financing Receivables Not Impaired | Watch obligors | Domestic | Retail | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	76,161	81,550
Financing Receivables Not Impaired | Watch obligors | Domestic | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5],[6]	7,602	123,087
Financing Receivables Not Impaired | Watch obligors | Domestic | Other | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5],[6]	522	246
Financing Receivables Not Impaired | Watch obligors | Domestic | Other | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5],[6]		55
Financing Receivables Not Impaired | Watch obligors | Domestic | Other | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5],[6]	489	476
Financing Receivables Not Impaired | Watch obligors | Domestic | Other | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[2],[5],[6]	5,447	121,201
Financing Receivables Not Impaired | Watch obligors | Domestic | Other | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5],[6]	1,144	1,109
Financing Receivables Not Impaired | Watch obligors | Foreign | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		365,418	426,599
Financing Receivables Not Impaired | Watch obligors | Foreign | Corporate | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		23,389	28,126
Financing Receivables Not Impaired | Watch obligors | Foreign | Corporate | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		341,687	398,231
Financing Receivables Not Impaired | Watch obligors | Foreign | Corporate | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		342	242
Financing Receivables Not Impaired | Watch obligors | Foreign | Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	65	6
Financing Receivables Not Impaired | Watch obligors | Foreign | Retail | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[4],[6]	65	6
Financing Receivables Not Impaired | Watch obligors | Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5],[6]	44,673	66,297
Financing Receivables Not Impaired | Watch obligors | Foreign | Other | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5],[6]	43,503	64,950
Financing Receivables Not Impaired | Watch obligors | Foreign | Other | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[5],[6]	1,170	1,347
Financing Receivables Impaired | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		567,844	615,260
Financing Receivables Impaired | Impaired loans | Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		488,284	505,631
Financing Receivables Impaired | Impaired loans | Domestic | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		117,579	142,070
Financing Receivables Impaired | Impaired loans | Domestic | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		39,655	40,833
Financing Receivables Impaired | Impaired loans | Domestic | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		71,389	58,075
Financing Receivables Impaired | Impaired loans | Domestic | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		127,082	130,884
Financing Receivables Impaired | Impaired loans | Domestic | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		30,858	27,527
Financing Receivables Impaired | Impaired loans | Domestic | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		9,371	12,341
Financing Receivables Impaired | Impaired loans | Domestic | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	[2]	5,434	3,739
Financing Receivables Impaired | Impaired loans | Domestic | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		86,916	90,162
Financing Receivables Impaired | Impaired loans | Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		79,560	109,629
Financing Receivables Impaired | Impaired loans | Foreign | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		9
Financing Receivables Impaired | Impaired loans | Foreign | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		1,803	1,819
Financing Receivables Impaired | Impaired loans | Foreign | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		76,448	106,650
Financing Receivables Impaired | Impaired loans | Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding		¥ 1,300	¥ 1,160
[1]	Amounts represent loan balances before deducting unearned income and deferred loan fees.
[2]	Other industries of Domestic includes trade receivables and lease receivables of consolidated VIEs.
[3]	The majority of Total foreign consist of Commercial and Industrial loans.
[4]	Amounts represent small balance, homogeneous loans which are subject to pool allocations.
[5]	Non-impaired loans held by subsidiaries other than MHBK and MHTB constitute Other, since their portfolio segments are not identical to those of MHBK and MHTB.
[6]	Special attention obligors are watch obligors with debt in TDR or 90 days or more delinquent debt. Loans to such obligors are considered impaired.

Loans (Impaired Loans Informati

Loans (Impaired Loans Information) (Detail) - JPY (¥) ¥ in Millions		6 Months Ended	12 Months Ended
		Sep. 30, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	¥ 434,131	¥ 478,527
Recorded investment not requiring an allowance for loan losses	[1],[2]	133,713	136,733
Total		567,844	615,260
Unpaid principal balance		614,914	664,870
Related allowance	[3]	132,180	152,513
Average recorded investment		591,552	756,205
Interest income recognized	[4]	3,771	8,091
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	401,540	415,181
Recorded investment not requiring an allowance for loan losses	[1],[2]	86,744	90,450
Total		488,284	505,631
Unpaid principal balance		521,702	539,541
Related allowance	[3]	118,323	124,180
Average recorded investment		496,957	604,617
Interest income recognized	[4]	3,254	7,049
Domestic | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	111,026	135,083
Recorded investment not requiring an allowance for loan losses	[1],[2]	6,553	6,987
Total		117,579	142,070
Unpaid principal balance		122,029	146,857
Related allowance	[3]	40,969	45,750
Average recorded investment		129,824	218,899
Interest income recognized	[4]	714	1,869
Domestic | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	30,818	31,557
Recorded investment not requiring an allowance for loan losses	[1],[2]	8,837	9,276
Total		39,655	40,833
Unpaid principal balance		47,362	48,752
Related allowance	[3]	4,032	4,411
Average recorded investment		40,244	49,926
Interest income recognized	[4]	240	516
Domestic | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	62,557	48,691
Recorded investment not requiring an allowance for loan losses	[1],[2]	8,832	9,384
Total		71,389	58,075
Unpaid principal balance		76,953	64,348
Related allowance	[3]	17,226	13,305
Average recorded investment		64,732	60,198
Interest income recognized	[4]	493	919
Domestic | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	117,212	119,463
Recorded investment not requiring an allowance for loan losses	[1],[2]	9,870	11,421
Total		127,082	130,884
Unpaid principal balance		136,833	139,556
Related allowance	[3]	39,610	42,798
Average recorded investment		128,983	139,333
Interest income recognized	[4]	905	1,842
Domestic | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	28,043	25,019
Recorded investment not requiring an allowance for loan losses	[1],[2]	2,815	2,508
Total		30,858	27,527
Unpaid principal balance		31,814	28,480
Related allowance	[3]	8,688	6,862
Average recorded investment		29,193	25,672
Interest income recognized	[4]	198	370
Domestic | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	5,545	8,392
Recorded investment not requiring an allowance for loan losses	[1],[2]	3,826	3,949
Total		9,371	12,341
Unpaid principal balance		9,371	12,341
Related allowance	[3]	813	3,176
Average recorded investment		10,856	8,648
Interest income recognized	[4]	47	78
Domestic | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	5,357	3,650
Recorded investment not requiring an allowance for loan losses	[1],[2]	77	89
Total		5,434	3,739
Unpaid principal balance		5,565	3,869
Related allowance	[3]	4,000	3,563
Average recorded investment		4,586	4,537
Interest income recognized	[4]	15	53
Domestic | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1]	40,982	43,326
Recorded investment not requiring an allowance for loan losses	[1],[2]	45,934	46,836
Total		86,916	90,162
Unpaid principal balance		91,775	95,338
Related allowance	[3]	2,985	4,315
Average recorded investment		88,539	97,404
Interest income recognized	[4]	642	1,402
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment requiring an allowance for loan losses	[1],[5]	32,591	63,346
Recorded investment not requiring an allowance for loan losses	[1],[2],[5]	46,969	46,283
Total	[5]	79,560	109,629
Unpaid principal balance	[5]	93,212	125,329
Related allowance	[3],[5]	13,857	28,333
Average recorded investment	[5]	94,595	151,588
Interest income recognized	[4],[5]	¥ 517	¥ 1,042
[1]	Amounts represent the outstanding balances of nonaccrual loans. The MHFG Group's policy for placing loans in nonaccrual status 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 the allowance for groups of loans which were collectively evaluated for impairment, in addition to the allowance for those loans that were individually evaluated for impairment. The total carrying amount of the groups of loans which were collectively evaluated for impairment at March 31, 2018 and September 30, 2018 was ¥245,809 million and ¥252,407 million, respectively.
[4]	Amounts represent the amount of interest income on impaired loans recognized on a cash basis and included in Interest income on loans in the consolidated statements of income.
[5]	The majority of Total foreign consist of Commercial and Industrial loans.

Loans (Impaired Loans Informa_2

Loans (Impaired Loans Information) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions	Sep. 30, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment	¥ 567,844	¥ 615,260
Small balance homogeneous loans of which were collectively evaluated for impairment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment	¥ 252,407	¥ 245,809

Loans (Troubled Debt Restructur

Loans (Troubled Debt Restructurings Entered Modified Periods by Type of Concession Granted) (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Modifications [Line Items]
Loan forgiveness or debt to equity swaps Recorded investment	[1]	¥ 1,008
Loan forgiveness or debt to equity swaps charge-off		2,012
Interest rate reduction and/or postponement of principal and/or interest		203,239	¥ 194,648
Domestic
Financing Receivable, Modifications [Line Items]
Interest rate reduction and/or postponement of principal and/or interest		193,746	181,345
Domestic | Manufacturing
Financing Receivable, Modifications [Line Items]
Interest rate reduction and/or postponement of principal and/or interest		51,161	55,611
Domestic | Construction and real estate
Financing Receivable, Modifications [Line Items]
Interest rate reduction and/or postponement of principal and/or interest		7,764	9,045
Domestic | Services
Financing Receivable, Modifications [Line Items]
Interest rate reduction and/or postponement of principal and/or interest		29,203	18,740
Domestic | Wholesale and retail
Financing Receivable, Modifications [Line Items]
Interest rate reduction and/or postponement of principal and/or interest		75,593	74,625
Domestic | Transportation and communications
Financing Receivable, Modifications [Line Items]
Interest rate reduction and/or postponement of principal and/or interest		13,999	12,244
Domestic | Banks and other financial institutions
Financing Receivable, Modifications [Line Items]
Interest rate reduction and/or postponement of principal and/or interest		7,160	3,461
Domestic | Individuals
Financing Receivable, Modifications [Line Items]
Interest rate reduction and/or postponement of principal and/or interest		8,866	7,619
Foreign
Financing Receivable, Modifications [Line Items]
Loan forgiveness or debt to equity swaps Recorded investment	[1],[2]	1,008
Loan forgiveness or debt to equity swaps charge-off	[2]	2,012
Interest rate reduction and/or postponement of principal and/or interest	[2]	¥ 9,493	¥ 13,303
[1]	Amounts represent the book values of loans immediately after the restructurings.
[2]	The majority of Total foreign consist of Commercial and Industrial loans.

Loans (Payment Defaults Occurre

Loans (Payment Defaults Occurred During Periods with Respect to Loans Modified as Troubled Debt Restructurings within Previous Six Months) (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Modifications [Line Items]
Recorded investment	¥ 10,837	¥ 23,856
Domestic
Financing Receivable, Modifications [Line Items]
Recorded investment	10,837	19,268
Domestic | Manufacturing
Financing Receivable, Modifications [Line Items]
Recorded investment	383	2,006
Domestic | Construction and real estate
Financing Receivable, Modifications [Line Items]
Recorded investment	390	70
Domestic | Services
Financing Receivable, Modifications [Line Items]
Recorded investment	714	2,561
Domestic | Wholesale and retail
Financing Receivable, Modifications [Line Items]
Recorded investment	6,700	13,396
Domestic | Transportation and communications
Financing Receivable, Modifications [Line Items]
Recorded investment	409	201
Domestic | Other industries
Financing Receivable, Modifications [Line Items]
Recorded investment		130
Domestic | Individuals
Financing Receivable, Modifications [Line Items]
Recorded investment	¥ 2,241	904
Foreign
Financing Receivable, Modifications [Line Items]
Recorded investment		¥ 4,588

Loans (Age Analysis of Past Due

Loans (Age Analysis of Past Due Loans) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		¥ 172,547	¥ 179,741
Current		84,808,002	83,481,599
Total	[1]	84,980,549	83,661,340
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		130,480	137,078
Current		56,332,613	58,523,436
Total		56,463,093	58,660,514
Domestic | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		8,724	9,092
Current		8,460,716	8,147,249
Total		8,469,440	8,156,341
Domestic | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		28,757	30,748
Current		8,447,077	8,070,920
Total		8,475,834	8,101,668
Domestic | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		6,141	8,170
Current		5,282,430	5,015,848
Total		5,288,571	5,024,018
Domestic | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		10,288	9,426
Current		5,158,120	5,103,247
Total		5,168,408	5,112,673
Domestic | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		2,323	2,823
Current		3,708,667	3,562,046
Total		3,710,990	3,564,869
Domestic | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		96	1,301
Current		4,455,242	4,470,122
Total		4,455,338	4,471,423
Domestic | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current		5,776,149	8,882,125
Total		5,776,149	8,882,125
Domestic | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		45	82
Current		5,059,846	5,018,305
Total	[2]	5,059,891	5,018,387
Domestic | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		74,106	75,436
Current		9,984,366	10,253,574
Total		10,058,472	10,329,010
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	[3]	42,067	42,663
Current	[3]	28,475,389	24,958,163
Total	[3]	28,517,456	25,000,826
Foreign | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		8,527,586	7,465,140
Foreign | Government and public institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		625,263	302,891
30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		36,608	38,759
30-59 Days Past Due | Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		35,732	37,862
30-59 Days Past Due | Domestic | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		594	585
30-59 Days Past Due | Domestic | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		1,461	1,641
30-59 Days Past Due | Domestic | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		1,006	1,977
30-59 Days Past Due | Domestic | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		2,829	1,704
30-59 Days Past Due | Domestic | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		53	356
30-59 Days Past Due | Domestic | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		90
30-59 Days Past Due | Domestic | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due			33
30-59 Days Past Due | Domestic | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		29,699	31,566
30-59 Days Past Due | Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	[3]	876	897
60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		16,773	17,997
60-89 Days Past Due | Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		16,425	17,547
60-89 Days Past Due | Domestic | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		416	470
60-89 Days Past Due | Domestic | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		927	474
60-89 Days Past Due | Domestic | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		1,014	1,142
60-89 Days Past Due | Domestic | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		833	1,083
60-89 Days Past Due | Domestic | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		707	639
60-89 Days Past Due | Domestic | Banks and other financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		6	1,301
60-89 Days Past Due | Domestic | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due			12
60-89 Days Past Due | Domestic | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		12,522	12,426
60-89 Days Past Due | Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	[3]	348	450
90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		119,166	122,985
90 Days or More Past Due | Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		78,323	81,669
90 Days or More Past Due | Domestic | Manufacturing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		7,714	8,037
90 Days or More Past Due | Domestic | Construction and real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		26,369	28,633
90 Days or More Past Due | Domestic | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		4,121	5,051
90 Days or More Past Due | Domestic | Wholesale and retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		6,626	6,639
90 Days or More Past Due | Domestic | Transportation and communications
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		1,563	1,828
90 Days or More Past Due | Domestic | Other industries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		45	37
90 Days or More Past Due | Domestic | Individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		31,885	31,444
90 Days or More Past Due | Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	[3]	¥ 40,843	¥ 41,316
[1]	Amounts represent loan balances before deducting unearned income and deferred loan fees.
[2]	Other industries of Domestic includes trade receivables and lease receivables of consolidated VIEs.
[3]	The majority of Total foreign consist of Commercial and Industrial loans.

Allowance for Loan Losses (Chan

Allowance for Loan Losses (Changes in Allowance for Loan Losses, Allowance for Loan Losses and Loans Outstanding Disaggregated on Basis of Impairment Method, by Portfolio Segment) (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period		¥ 309,902	¥ 479,673
Provision (credit) for loan losses		(13,280)	(117,962)
Charge-offs		(31,264)	(21,218)
Recoveries		7,543	8,009
Net charge-offs		(23,721)	(13,209)
Others	[1]	1,588	1,967
Balance at end of period		274,489	350,469
Allowance for loan losses of which individually evaluated for impairment		115,443		¥ 139,774
Allowance for loan losses of which collectively evaluated for impairment		159,046		170,128
Loans	[2]	84,980,549		83,661,340
Loans of which individually evaluated for impairment	[2]	541,788		675,440
Loans of which collectively evaluated for impairment	[2]	84,438,761		82,985,900
Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period		249,072	407,327
Provision (credit) for loan losses		(13,435)	(109,379)
Charge-offs		(27,419)	(17,366)
Recoveries		4,914	6,447
Net charge-offs		(22,505)	(10,919)
Others	[1]	2,519	2,552
Balance at end of period		215,651	289,581
Allowance for loan losses of which individually evaluated for impairment		105,988		129,789
Allowance for loan losses of which collectively evaluated for impairment		109,663		119,283
Loans	[2]	65,256,236		60,837,559
Loans of which individually evaluated for impairment	[2]	474,645		593,053
Loans of which collectively evaluated for impairment	[2]	64,781,591		60,244,506
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period		28,192	36,923
Provision (credit) for loan losses		(2,290)	(6,469)
Charge-offs		(1,243)	(745)
Recoveries		220	315
Net charge-offs		(1,023)	(430)
Balance at end of period		24,879	30,024
Allowance for loan losses of which individually evaluated for impairment		2,501		2,602
Allowance for loan losses of which collectively evaluated for impairment		22,378		25,590
Loans	[2]	10,837,056		11,133,862
Loans of which individually evaluated for impairment	[2]	21,723		21,364
Loans of which collectively evaluated for impairment	[2]	10,815,333		11,112,498
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period		32,638	35,423
Provision (credit) for loan losses		2,445	(2,114)
Charge-offs		(2,602)	(3,107)
Recoveries		2,409	1,247
Net charge-offs		(193)	(1,860)
Others	[1]	(931)	(585)
Balance at end of period		33,959	¥ 30,864
Allowance for loan losses of which individually evaluated for impairment		6,954		7,383
Allowance for loan losses of which collectively evaluated for impairment		27,005		25,255
Loans	[2]	8,887,257		11,689,919
Loans of which individually evaluated for impairment	[2]	45,420		61,023
Loans of which collectively evaluated for impairment	[2]	¥ 8,841,837		¥ 11,628,896
[1]	Others includes primarily foreign exchange translation.
[2]	Amounts represent loan balances before deducting unearned income and deferred loan fees.

Other Assets and Liabilities (D

Other Assets and Liabilities (Details of Other Assets and Liabilities) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Other assets:
Receivables from brokers, dealers and customers for securities transactions	[1]	¥ 1,356,005	¥ 1,578,952
Other		364,631	368,030
Collateral pledged for derivative transactions		868,572	981,390
Margins provided for futures contracts		171,927	142,156
Other		906,646	965,137
Prepaid pension cost		859,484	874,191
Security deposits		125,739	126,001
Loans held for sale		15,758	86,153
Other		557,763	609,624
Total		5,226,525	5,731,634
Other liabilities:
Payables to brokers, dealers and customers for securities transactions	[1]	1,986,580	1,410,785
Other		556,064	455,789
Guaranteed trust principal	[2]	780,619	761,685
Collateral accepted for derivative transactions		700,758	598,524
Margins accepted for futures contracts		333,238	325,038
Unearned income	[3]	132,364	130,916
Other		905,459	1,022,858
Total		¥ 5,395,082	¥ 4,705,595
[1]	Receivables from brokers, dealers and customers for securities transactions included ¥372,395 million and ¥372,799 million of such receivables of consolidated VIEs at March 31, 2018 and September 30, 2018, respectively. Payables to brokers, dealers and customers for securities transactions included ¥422,060 million and ¥446,935 million of such payables of consolidated VIEs at March 31, 2018 and September 30, 2018, respectively.
[2]	Guaranteed trust principal is the liability of certain consolidated trust arrangements that meet the definition of a VIE for which the MHFG Group provides guarantees for the repayment of principal. See Note 15 "Variable interest entities and securitizations" for further discussion of the guaranteed principal money trusts.
[3]	Unearned income is primarily comprised of loan fees received from consumer loan customers when loans are made. This income is being deferred and recognized in earnings over the life of the loan.

Other Assets and Liabilities _2

Other Assets and Liabilities (Details of Other Assets and Liabilities) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Other Assets and Other Liabilities [Line Items]
Accounts receivable from brokers, dealers and customers for securities transactions	[1]	¥ 1,356,005	¥ 1,578,952
Accounts payable to brokers, dealers and customers for securities transactions	[1]	1,986,580	1,410,785
Consolidated VIEs
Other Assets and Other Liabilities [Line Items]
Accounts receivable from brokers, dealers and customers for securities transactions		372,799	372,395
Accounts payable to brokers, dealers and customers for securities transactions		¥ 446,935	¥ 422,060
[1]	Receivables from brokers, dealers and customers for securities transactions included ¥372,395 million and ¥372,799 million of such receivables of consolidated VIEs at March 31, 2018 and September 30, 2018, respectively. Payables to brokers, dealers and customers for securities transactions included ¥422,060 million and ¥446,935 million of such payables of consolidated VIEs at March 31, 2018 and September 30, 2018, respectively.

Preferred and Common Stock (Com

Preferred and Common Stock (Composition of Preferred Stock) (Detail) - shares	Sep. 30, 2018	Mar. 31, 2018
Class Fourteen Preferred Stock
Class of Stock [Line Items]
Number of shares Authorized	900,000,000	900,000,000
Number of shares Issued	0	0
Class Fifteen Preferred Stock
Class of Stock [Line Items]
Number of shares Authorized	900,000,000	900,000,000
Number of shares Issued	0	0
Class Sixteen Preferred Stock
Class of Stock [Line Items]
Number of shares Authorized	1,500,000,000	1,500,000,000
Number of shares Issued	0	0

Preferred and Common Stock - Su

Preferred and Common Stock - Summary of Changes in Number of Issued Shares of Common Stock (Detail) - shares	6 Months Ended	12 Months Ended
	Sep. 30, 2018	Mar. 31, 2018
Class of Stock [Line Items]
Balance at beginning of period	25,389,644,945	25,386,307,945
Issuance of new shares of common stock due to exercise of stock acquisition rights	2,854,000	3,337,000
Balance at end of period	25,392,498,945	25,389,644,945

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Changes in Each Component of AOCI) (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		¥ 9,503,700
Pension liability adjustments:		0	¥ 0
Less: reclassification adjustments for losses (gains) included in net income		(3,800)
Change during period		(19,030)	165,077
Balance at end of fiscal year		9,831,837	9,200,761
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		1,741,894	1,521,163
Cumulative effect of change in accounting principles		(1,535,142)
Balance at beginning of period, adjusted		206,752	1,521,163
Change during period		(18,837)	164,684
Balance at end of fiscal year		187,915	1,685,847
Net unrealized gains (losses) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		1,556,585	1,461,302
Cumulative effect of change in accounting principles		(1,525,064)
Balance at beginning of period, adjusted		31,521	1,461,302
Unrealized gains (losses) during period		(25,155)	247,493
Less: reclassification adjustments for losses (gains) included in net income		(862)	(78,659)
Change during period		(26,017)	168,834
Balance at end of fiscal year		5,504	1,630,136
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(35,076)	(5,535)
Foreign currency translation adjustments during period		7,678	(4,322)
Change during period		7,678	(4,322)
Balance at end of fiscal year		(27,398)	(9,857)
Pension liability adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		220,385	65,396
Unrealized gains (losses) during period		(218)	32
Less: reclassification adjustments for losses (gains) included in net income		(2,916)	140
Change during period		(3,134)	172
Balance at end of fiscal year		217,251	¥ 65,568
Accumulated Own Credit Risk Adjustment Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of change in accounting principles	[1]	(10,078)
Balance at beginning of period, adjusted	[1]	(10,078)
Unrealized gains (losses) during period	[1]	2,656
Less: reclassification adjustments for losses (gains) included in net income	[1]	(20)
Change during period	[1]	2,636
Balance at end of fiscal year	[1]	¥ (7,442)
[1]	The MHFG Group adopted ASU No.2016-01 on April 1, 2018. The ASU requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. See Note 2 "Recently issued accounting pronouncements" for further details.

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Amounts Reclassified Out of Accumulated Other Comprehensive Income into Net Income) (Detail) ¥ in Millions	6 Months Ended
	Sep. 30, 2018JPY (¥)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Before tax	¥ 5,376	[1]
Tax effect	(1,576)	[2]
Net of tax before allocation to noncontrolling interests	3,800
Net of tax attributable to noncontrolling interests	(2)	[2]
Net of tax attributable to MHFG shareholders	3,798
Accumulated Net Unrealized Investment Gain (Loss) | Gain (Loss) on Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Before tax	1,245	[1]
Tax effect	(383)	[2]
Net of tax before allocation to noncontrolling interests	862
Net of tax attributable to MHFG shareholders	862
Accumulated Defined Benefit Plans Adjustment | Salaries and employee benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Before tax	4,102	[1]
Tax effect	(1,184)	[2]
Net of tax before allocation to noncontrolling interests	2,918
Net of tax attributable to noncontrolling interests	(2)	[2]
Net of tax attributable to MHFG shareholders	2,916
Accumulated Own Credit Risk Adjustment | Other Noninterest Income (Expenses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Before tax	29	[1]
Tax effect	(9)	[2]
Net of tax before allocation to noncontrolling interests	20
Net of tax attributable to MHFG shareholders	¥ 20
[1]	The amounts in the Before tax column are recorded in each account presented under the heading "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 (loss) attributable to noncontrolling interests in the consolidated statements of income, respectively.

Regulatory Matters (Capital Ade

Regulatory Matters (Capital Adequacy Ratios of MHFG, MHBK, and MHTB Calculated in Accordance with Japanese GAAP and Guidelines Established by Financial Services Agency) (Detail) - JPY (¥) ¥ in Billions		Sep. 30, 2018	Mar. 31, 2018
Mizuho Financial Group Inc | Consolidated
Common Equity Tier 1 capital:
Required	[1]	¥ 4,304	¥ 4,247
Actual		7,607	7,437
Required	[1]	5,208	5,140
Actual		¥ 9,435	¥ 9,192
Required	[1]	8.645%	8.635%
Actual		15.66%	15.44%
Required	[1]	¥ 6,413	¥ 6,331
Actual		¥ 11,214	¥ 10,860
Required	[1]	10.645%	10.635%
Actual		18.61%	18.24%
Common Equity Tier 1 capital:
Required	[1]	7.145%	7.135%
Actual		12.62%	12.49%
Mizuho Bank Limited | Consolidated
Common Equity Tier 1 capital:
Required		¥ 2,470	¥ 2,400
Actual		6,817	6,584
Required		3,294	3,200
Actual		¥ 8,638	¥ 8,330
Required		6.00%	6.00%
Actual		15.73%	15.61%
Required		¥ 4,391	¥ 4,267
Actual		¥ 10,331	¥ 9,881
Required		8.00%	8.00%
Actual		18.82%	18.52%
Common Equity Tier 1 capital:
Required		4.50%	4.50%
Actual		12.41%	12.34%
Mizuho Bank Limited | Non-consolidated
Common Equity Tier 1 capital:
Required		¥ 2,374	¥ 2,312
Actual		6,495	6,330
Required		3,165	3,082
Actual		¥ 8,322	¥ 8,081
Required		6.00%	6.00%
Actual		15.77%	15.73%
Required		¥ 4,220	¥ 4,109
Actual		¥ 10,007	¥ 9,619
Required		8.00%	8.00%
Actual		18.97%	18.72%
Common Equity Tier 1 capital:
Required		4.50%	4.50%
Actual		12.31%	12.32%
Mizuho Trust & Banking Company Limited | Consolidated
Common Equity Tier 1 capital:
Required		¥ 111	¥ 112
Actual		522	498
Required		147	149
Actual		¥ 523	¥ 499
Required		6.00%	6.00%
Actual		21.27%	20.05%
Required		¥ 196	¥ 199
Actual		¥ 527	¥ 505
Required		8.00%	8.00%
Actual		21.46%	20.28%
Common Equity Tier 1 capital:
Required		4.50%	4.50%
Actual		21.25%	19.99%
Mizuho Trust & Banking Company Limited | Non-consolidated
Common Equity Tier 1 capital:
Required		¥ 110	¥ 112
Actual		520	504
Required		147	149
Actual		¥ 520	¥ 504
Required		6.00%	6.00%
Actual		21.26%	20.28%
Required		¥ 196	¥ 199
Actual		¥ 524	¥ 509
Required		8.00%	8.00%
Actual		21.45%	20.50%
Common Equity Tier 1 capital:
Required		4.50%	4.50%
Actual		21.26%	20.28%
[1]	The required ratios disclosed above, at March 31, 2018 and September 30, 2018, include the transitional capital conservation buffer of 1.875%, the countercyclical capital buffer of 0.01% and 0.02%, respectively, and the transitional additional loss absorbency requirements for global systemically important banks ("G-SIBs") and domestic systemically important banks ("D-SIBs") of 0.75%, which are all in addition to the regulatory minima. The respective required amounts are determined by applying the ratios to the sum of the risk weighted assets and certain other risk amounts.

Regulatory Matters (Capital A_2

Regulatory Matters (Capital Adequacy Ratios of MHFG, MHBK, and MHTB Calculated in Accordance with Japanese GAAP and Guidelines Established by Financial Services Agency) (Parenthetical) (Detail)	6 Months Ended	12 Months Ended
	Sep. 30, 2018	Mar. 31, 2018
Japan Gaap Schedule Of Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Capital conservation buffer	1.875%	1.875%
Additional loss absorbency requirements for G-SIBs and D-SIBs	0.75%	0.75%
Countercyclical capital buffer	0.02%	0.01%

Earnings Per Common Share (Comp

Earnings Per Common Share (Computation of Basic and Diluted Earnings Per Common Share) (Detail) - JPY (¥) ¥ / shares in Units, shares in Thousands, ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Net income:
Net income attributable to MHFG common shareholders	¥ 285,270	¥ 372,549
Effect of dilutive securities
Net income attributable to common shareholders after assumed conversions	¥ 285,270	¥ 372,549
Shares:
Weighted average common shares outstanding	25,363,167	25,366,347
Effect of dilutive securities:
Stock options	4,790	7,933
Weighted average common shares after assumed conversions	25,367,957	25,374,280
Amounts per common share:
Basic net income per common share	¥ 11.25	¥ 14.69
Diluted net income per common share	¥ 11.25	¥ 14.68

Income Taxes (Components of Inc

Income Taxes (Components of Income Tax Expense) (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of Provision of Income Taxes [Line Items]
Current tax expense	¥ 114,666	¥ 99,238
Deferred tax expense (benefit)	(28,961)	20,095
Total income tax expense	¥ 85,705	¥ 119,333

Income Taxes (Detailed Amounts

Income Taxes (Detailed Amounts of Tax Effects of Items Recorded Directly in Equity) (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Net unrealized gains (losses) on available-for-salesecurities:
Unrealized gains (losses)		¥ (11,292)	¥ 105,819
Less: reclassification adjustments		(383)	(35,053)
Total		(11,675)	70,766
Pension liability adjustments:
Unrealized gains (losses)		(97)	11
Less: reclassification adjustments		(1,184)	96
Total		(1,281)	107
Own credit risk adjustments:
Unrealized gains (losses)	[1]	967
Less: reclassification adjustments	[1]	(9)
Total	[1]	958
Total tax effect before allocation to noncontrolling interests		¥ (11,998)	¥ 70,873
[1]	The MHFG Group adopted ASU No.2016-01 on April 1, 2018. The ASU requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. See Note 2 "Recently issued accounting pronouncements" for further details.

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Income Taxes [Line Items]
Statutory tax rate	30.62%	30.86%
Effective tax rate	20.52%	23.27%
Net operating loss carryforwards	¥ 720,000
Unrecognized Tax Benefits	¥ 2,965

Pension and Other Employee Be_3

Pension and Other Employee Benefit Plans (Components of Net Periodic Costs of Severance Indemnities and Pension Plans) (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost-benefits earned during the period	¥ 21,726	¥ 21,643
Interest costs on projected benefit obligations	3,331	3,609
Expected return on plan assets	(19,124)	(17,353)
Amortization of prior service benefits	76	102
Amortization of net actuarial loss (gain)	(3,942)	214
Special termination benefits	1,792	2,128
Net periodic benefit cost	¥ 3,859	¥ 10,343

Pension and Other Employee Be_4

Pension and Other Employee Benefit Plans - Additional Information (Detail) - JPY (¥) ¥ in Billions	6 Months Ended
	Sep. 30, 2018	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Pension plan, contribution expected to be paid during the next fiscal year		¥ 52
Total payment to pension plans	¥ 26
Additional contribution expected to be paid during remainder of fiscal year	¥ 26

Derivative Financial Instrume_3

Derivative Financial Instruments (Summary of Notional and Fair Value Amounts of Derivative Instruments Outstanding) (Detail) - JPY (¥) ¥ in Billions		Sep. 30, 2018	Mar. 31, 2018
Derivatives, Fair Value [Line Items]
Notional amount	[1]	¥ 1,219,816	¥ 1,169,233
Interest rate contracts
Derivatives, Fair Value [Line Items]
Notional amount	[1]	1,057,838	1,004,169
Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Notional amount	[1]	152,512	155,832
Equity-related contracts
Derivatives, Fair Value [Line Items]
Notional amount	[1]	6,201	6,189
Credit-related contracts
Derivatives, Fair Value [Line Items]
Notional amount	[1]	2,909	2,708
Other contracts
Derivatives, Fair Value [Line Items]
Notional amount	[1]	356	335
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value of derivative receivables	[2]		2
Fair value of derivative payables	[2]		9
Designated as Hedging Instrument | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative receivables	[2]		2
Designated as Hedging Instrument | Equity-related contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative payables	[2]		9
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value of derivative receivables	[2]	7,360	10,109
Fair value of derivative payables	[2]	6,936	9,707
Not Designated as Hedging Instrument | Interest rate contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative receivables	[2]	4,607	7,176
Fair value of derivative payables	[2]	4,520	7,143
Not Designated as Hedging Instrument | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative receivables	[2]	2,367	2,695
Fair value of derivative payables	[2]	2,134	2,382
Not Designated as Hedging Instrument | Equity-related contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative receivables	[2]	315	197
Fair value of derivative payables	[2]	214	142
Not Designated as Hedging Instrument | Credit-related contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative receivables	[2]	22	18
Fair value of derivative payables	[2]	22	21
Not Designated as Hedging Instrument | Other contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative receivables	[2]	49	23
Fair value of derivative payables	[2]	¥ 46	¥ 19
[1]	Notional amount includes 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.

Derivative Financial Instrume_4

Derivative Financial Instruments - Additional Information (Detail) - JPY (¥) ¥ in Millions	Sep. 30, 2018	Mar. 31, 2018
Derivative [Line Items]
Cash collateral provided and not offset against derivative positions and included in Other assets	¥ 868,572	¥ 981,390
Cash collateral accepted and not offset against derivative positions and included in Other liabilities	¥ 700,758	¥ 598,524

Derivative Financial Instrume_5

Derivative Financial Instruments (Summary of Gains and Losses Information Related to Fair Value Hedges) (Detail) ¥ in Millions	6 Months Ended
	Sep. 30, 2017JPY (¥)
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income- Derivatives	¥ (22,493)
Gains (losses) recorded in income- Hedged items	20,208
Gains (losses) recorded in income- Hedge ineffectiveness	0
Gains (losses) recorded in income- Net gain (loss) excluded from assessment of effectiveness	(2,285)
Equity-related contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income- Derivatives	(22,493)
Gains (losses) recorded in income- Hedged items	20,208
Gains (losses) recorded in income- Hedge ineffectiveness	0
Gains (losses) recorded in income- Net gain (loss) excluded from assessment of effectiveness	¥ (2,285)

Derivative Financial Instrume_6

Derivative Financial Instruments (Summary of Gains and Losses Information Related to Net Investment Hedges) (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion recorded in OCI	¥ 1,937	¥ 3,487
Ineffective portion recorded in income	(32)	196
Financial instruments hedging foreign exchange risk
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion recorded in OCI	1,937	3,487
Ineffective portion recorded in income	¥ (32)	¥ 196

Derivative Financial Instrume_7

Derivative Financial Instruments (Summary of Gains and Losses Information Related to Net Investment Hedges) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions	Sep. 30, 2018	Sep. 30, 2017
Financial instruments hedging foreign exchange risk
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated other comprehensive income reclassified to earnings	¥ 186	¥ 0

Derivative Financial Instrume_8

Derivative Financial Instruments (Summary of Gains and Losses on Derivatives not Designated or Qualifying as Hedges) (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income		¥ (29,006)	¥ (22,609)
Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income		(75,324)	26,648
Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income		26,706	(4,511)
Equity-related contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income	[1]	20,432	(41,869)
Credit-related contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income	[2]	(35)	(3,371)
Other contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income		¥ (785)	¥ 494
[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 gain (loss) of ¥(273) million and ¥(215) million on the credit derivatives economically managing the credit risk of loans during the six months ended September 30, 2017 and 2018, respectively.

Derivative Financial Instrume_9

Derivative Financial Instruments (Summary of Gains and Losses on Derivatives not Designated or Qualifying as Hedges) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income		¥ (29,006)	¥ (22,609)
Credit-related contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income	[1]	(35)	(3,371)
Credit-related contracts | Loans related to credit derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in income		¥ (215)	¥ (273)
[1]	Amounts include the net gain (loss) of ¥(273) million and ¥(215) million on the credit derivatives economically managing the credit risk of loans during the six months ended September 30, 2017 and 2018, respectively.

Derivative Financial Instrum_10

Derivative Financial Instruments (Summary of Notional and Fair Value Amounts of Credit Derivatives) (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2018	Mar. 31, 2018
Credit protection written
Credit Derivatives [Line Items]
Notional amount	¥ 1,434	¥ 1,302
Fair value	19	19
Credit protection written | Investment grade
Credit Derivatives [Line Items]
Notional amount	1,182	1,105
Fair value	14	15
Credit protection written | Non-investment grade
Credit Derivatives [Line Items]
Notional amount	252	197
Fair value	5	4
Credit protection purchased
Credit Derivatives [Line Items]
Notional amount	1,627	1,541
Fair value	¥ (19)	¥ (22)

Derivative Financial Instrum_11

Derivative Financial Instruments (Maximum Potential Amount of Future Payments for Credit Protection Written by Expiration Period) (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2018	Mar. 31, 2018
Credit Derivatives [Line Items]
Maximum payout/Notional amount	¥ 1,434	¥ 1,302
One year or less
Credit Derivatives [Line Items]
Maximum payout/Notional amount	322	329
After one year through five years
Credit Derivatives [Line Items]
Maximum payout/Notional amount	927	831
After five years
Credit Derivatives [Line Items]
Maximum payout/Notional amount	¥ 185	¥ 142

Derivative Financial Instrum_12

Derivative Financial Instruments (Quantitative Information about Derivative Instruments with Credit-risk-related Contingent Features) (Detail) - JPY (¥) ¥ in Billions		Sep. 30, 2018	Mar. 31, 2018
Credit Derivatives [Line Items]
Aggregate fair value of derivative instruments with credit-risk-related contingent features in net liability positions		¥ 548	¥ 572
Collateral provided to counterparties in the normal course of business		514	593
Amount required to be posted as collateral or settled immediately if credit-risk-related contingent features were triggered	[1]	¥ 34	¥ 0
[1]	There was no amount that the Group would be required to post as collateral or settle immediately on March 31, 2018.

Derivative Financial Instrum_13

Derivative Financial Instruments (Quantitative Information about Derivative Instruments with Credit-risk-related Contingent Features) (Parenthetical) (Detail) - JPY (¥) ¥ in Billions		Sep. 30, 2018	Mar. 31, 2018
Credit Derivatives [Line Items]
Amount required to be posted as collateral or settled immediately if credit-risk-related contingent features were triggered	[1]	¥ 34	¥ 0
[1]	There was no amount that the Group would be required to post as collateral or settle immediately on March 31, 2018.

Commitments and Contingencies_2

Commitments and Contingencies (Summary of Maximum Potential Amount of Future Payments under Guarantees) (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2018	Mar. 31, 2018
Performance guarantees
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount	¥ 2,205	¥ 2,165
Guarantees on loans
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount	393	241
Guarantees on securities
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount	173	164
Other guarantees
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount	2,076	2,210
Guarantees for repayment of trust principal
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount	754	709
Liabilities of trust accounts
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount	12,172	13,861
Derivative financial instruments
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount	¥ 12,941	¥ 11,654

Commitments and Contingencies_3

Commitments and Contingencies (Summary of Maximum Potential Amount of Future Payments of Certain Guarantees Classified Based on Internal Ratings) (Detail) - Performance guarantees, Guarantees on loans, Guarantees on securities and Other guarantees - JPY (¥) ¥ in Billions		Sep. 30, 2018	Mar. 31, 2018
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount		¥ 4,847	¥ 4,780
Investment grade
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount	[1]	3,964	3,930
Non-investment grade
Guarantor Obligations [Line Items]
Maximum potential/Contractual or Notional amount		¥ 883	¥ 850
[1]	Investment grade in the internal rating scale generally corresponds to BBB- or above in the external rating scale.

Commitments and Contingencies_4

Commitments and Contingencies (Summary of Contractual Amounts with Regard to Undrawn Commitments) (Detail) - JPY (¥) ¥ in Billions		Sep. 30, 2018	Mar. 31, 2018
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance-sheet instruments, contractual amounts of the undrawn commitments		¥ 83,011	¥ 79,138
Commitments to Extend Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance-sheet instruments, contractual amounts of the undrawn commitments	[1]	82,194	78,448
Commercial letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance-sheet instruments, contractual amounts of the undrawn commitments		¥ 817	¥ 690
[1]	Commitments to extend credit include commitments to invest in securities.

Variable Interest Entities an_3

Variable Interest Entities and Securitizations (Consolidated Assets of Consolidated VIEs as well as Total Assets and Maximum Exposure to Loss for Significant Unconsolidated VIEs) (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2018	Mar. 31, 2018
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	¥ 5,962	¥ 5,868
Significant unconsolidated VIEs- Total assets	1,452	1,969
Significant unconsolidated VIEs- Maximum exposure to loss	445	538
Asset-backed commercial paper/loan programs
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	2,082	2,185
Asset-backed securitizations
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	573	627
Significant unconsolidated VIEs- Total assets	78	78
Significant unconsolidated VIEs- Maximum exposure to loss	9	5
Investments in securitization products
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	373	374
Investment funds
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	2,913	2,661
Significant unconsolidated VIEs- Total assets	1,374	1,891
Significant unconsolidated VIEs- Maximum exposure to loss	436	533
Trust arrangements and other
Variable Interest Entity [Line Items]
Consolidated VIEs- Consolidated assets	¥ 21	¥ 21

Variable Interest Entities an_4

Variable Interest Entities and Securitizations (Carrying Amounts and Classification of Assets and Liabilities on Consolidated Balance Sheets that Relate to Variable Interests in Significant Unconsolidated VIEs) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Assets on balance sheets related to unconsolidated VIEs:
Trading account assets		¥ 23,420,966	¥ 24,302,543
Loans		84,555,759	83,204,742
Total		204,178,804	204,255,642
Liabilities on balance sheets and maximum exposure to loss related to unconsolidated VIEs:
Payables under securities lending transactions		2,112,335	1,832,870
Trading account liabilities		9,744,238	13,115,270
Total		194,346,967	194,751,942
Maximum exposure to loss		445,000	538,000
Unconsolidated VIEs
Assets on balance sheets related to unconsolidated VIEs:
Trading account assets		95,000	89,000
Investments		136,000	210,000
Loans		133,000	163,000
Total		364,000	462,000
Liabilities on balance sheets and maximum exposure to loss related to unconsolidated VIEs:
Payables under securities lending transactions		42,000	38,000
Trading account liabilities		1,000	1,000
Total		43,000	39,000
Maximum exposure to loss	[1]	¥ 445,000	¥ 538,000
[1]	This represents the maximum amount the Group could possibly be required to record in its consolidated statements of income associated with on-balance-sheet exposures and off-balance-sheet liabilities such as undrawn commitments.

Variable Interest Entities an_5

Variable Interest Entities and Securitizations - Additional Information (Detail) - JPY (¥) ¥ in Millions	Sep. 30, 2018	Mar. 31, 2018
Variable Interest Entity [Line Items]
Long-term debt	¥ 13,533,141	¥ 12,955,230
Debt Instrument [Member]
Variable Interest Entity [Line Items]
Long-term debt	689,000	950,000
Assets associated with securitization transactions
Variable Interest Entity [Line Items]
Transferred assets continue to be carried on the consolidated balance sheets	198,000	208,000
Assets associated with loan participation transactions
Variable Interest Entity [Line Items]
Transferred assets continue to be carried on the consolidated balance sheets	¥ 101,000	¥ 89,000

Summary of Noninterest Income (

Summary of Noninterest Income (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Fee and commission income		¥ 413,727	¥ 401,231
Foreign exchange gains (losses)-net	[1]	44,718	50,765
Trading account gains (losses)-net	[2]	64,956	235,339
Investment gains (losses)-net		0	0
Debt securities	[1]	2,485	16,099
Equity securities	[1]	306,788	109,390
Equity in earnings (losses) of equity method investees-net	[1]	22,627	10,389
Gains on disposal of premises and equipment	[1]	4,305	4,567
Other noninterest income	[2]	48,950	33,158
Total noninterest income		908,556	860,938
Securities related business
Disaggregation of Revenue [Line Items]
Fee and commission income	[3]	79,138	85,897
Banking
Disaggregation of Revenue [Line Items]
Fee and commission income	[2]	70,647	65,081
Correspondent clearing
Disaggregation of Revenue [Line Items]
Fee and commission income	[3]	55,078	54,166
Investment advisory, management and administrative service
Disaggregation of Revenue [Line Items]
Fee and commission income	[3]	49,818	50,322
Fiduciary and trust
Disaggregation of Revenue [Line Items]
Fee and commission income	[3]	57,372	54,367
Agency business
Disaggregation of Revenue [Line Items]
Fee and commission income	[3]	19,509	18,261
Guarantee related business
Disaggregation of Revenue [Line Items]
Fee and commission income	[1]	14,234	13,899
Financial service, other
Disaggregation of Revenue [Line Items]
Fee and commission income	[3]	67,931	59,238
Financial service
Disaggregation of Revenue [Line Items]
Fee and commission income		¥ 413,727	¥ 401,231
[1]	These amounts are revenues from contracts that do not meet the scope of ASC 606.
[2]	Part of these amounts are considered to be revenues from contracts that are within the scope of ASC 606.
[3]	These amounts are revenues from contracts within the scope of ASC 606, "Revenue from contracts with customers" ("ASC 606").

Noninterest Income - Additional

Noninterest Income - Additional Information (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Other Revenues [Line Items]
Trust fees		¥ 26,000
Fees related to trust business		31,000
Trading account gains (losses)-net	[1]	64,956	¥ 235,339
Other noninterest income	[1]	48,950	¥ 33,158
Revenue from contracts with customers ("ASC 606")
Other Revenues [Line Items]
Trading account gains (losses)-net		31,000
Other noninterest income		¥ 14,000
[1]	Part of these amounts are considered to be revenues from contracts that are within the scope of ASC 606.

Fair Value - Additional Informa

Fair Value - Additional Information (Detail) - JPY (¥) ¥ in Billions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Carrying amounts of other equity interests of which fair value is not readily determinable	¥ 232		¥ 267
Senior borrowings and bonds
Fair Value Measurement Inputs and Valuation Techniques [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	33		¥ 21
Net unrealized gains (losses) resulting from changes in fair values of the notes	¥ 8	¥ (28)
Investment funds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Underlying assets, estimated remaining liquidation period	10 years
Long-term debt
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of assets transferred into Level 3	¥ 2
Fair value of liabilities transferred out of Level 3		10
Fair value of liabilities transferred into Level 3	2	1
Trading securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of assets transferred into Level 3		123
Fair value of assets transferred out of Level 3		240
Available-for-sale securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of assets transferred into Level 3	¥ 61	15
Fair value of assets transferred out of Level 3		¥ 29

Fair Value (Summary of Assets a

Fair Value (Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis, Including Fair Value Option Elected) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Assets:
Available-for-sale securities		¥ 20,471,615	¥ 23,665,628
Liabilities:
Long-term debt		2,380,034	1,955,636
Fair Value, Measurements, Recurring
Assets:
Equity securities with readily determinable fair values	[1]	4,503,000
Equity securities measured at net asset value	[1],[2]	35,000
Other investments		41,000	38,000
Total assets measured at fair value		48,471,000	48,007,000
Liabilities:
Trading securities sold, not yet purchased		2,808,000	3,399,000
Long-term debt	[3]	2,380,000	1,956,000
Total liabilities measured at fair value		12,124,000	15,071,000
Fair Value, Measurements, Recurring | Trading Account Asset
Assets:
Securities measured at net asset value	[2],[4]	661,000	705,000
Fair Value, Measurements, Recurring | Interest rate contracts
Assets:
Assets, derivatives		4,607,000	7,176,000
Liabilities:
Liabilities, derivatives		4,520,000	7,143,000
Fair Value, Measurements, Recurring | Foreign exchange contracts
Assets:
Assets, derivatives		2,367,000	2,697,000
Liabilities:
Liabilities, derivatives		2,134,000	2,382,000
Fair Value, Measurements, Recurring | Equity-related contracts
Assets:
Assets, derivatives		315,000	197,000
Liabilities:
Liabilities, derivatives		214,000	151,000
Fair Value, Measurements, Recurring | Credit-related contracts
Assets:
Assets, derivatives		22,000	18,000
Liabilities:
Liabilities, derivatives		22,000	21,000
Fair Value, Measurements, Recurring | Other contracts
Assets:
Assets, derivatives		49,000	23,000
Liabilities:
Liabilities, derivatives		46,000	19,000
Fair Value, Measurements, Recurring | Japanese government bonds
Assets:
Assets, trading securities	[4]	1,967,000	1,418,000
Available-for-sale securities		13,451,000	13,332,000
Fair Value, Measurements, Recurring | Japanese local government bonds
Assets:
Assets, trading securities	[4]	93,000	107,000
Available-for-sale securities		240,000	239,000
Fair Value, Measurements, Recurring | U.S. Treasury bonds and federal agency securities
Assets:
Assets, trading securities	[4]	2,857,000	2,651,000
Available-for-sale securities		1,134,000	686,000
Fair Value, Measurements, Recurring | Other foreign government bonds
Assets:
Assets, trading securities	[4]	2,197,000	2,162,000
Available-for-sale securities		1,243,000	1,058,000
Fair Value, Measurements, Recurring | Agency mortgage-backed securities
Assets:
Assets, trading securities	[4]	1,865,000	1,799,000
Available-for-sale securities		871,000	889,000
Fair Value, Measurements, Recurring | Residential mortgage-backed securities
Assets:
Assets, trading securities	[4]	12,000	12,000
Available-for-sale securities		109,000	119,000
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities
Assets:
Available-for-sale securities		469,000	441,000
Fair Value, Measurements, Recurring | Certificates of deposit and commercial paper
Assets:
Assets, trading securities	[4]	1,322,000	643,000
Fair Value, Measurements, Recurring | Corporate bonds and other debt securities
Assets:
Assets, trading securities	[4]	3,334,000	3,030,000
Fair Value, Measurements, Recurring | Equity securities
Assets:
Assets, trading securities	[4]	1,753,000	1,665,000
Fair Value, Measurements, Recurring | Japanese corporate bonds and other debt securities
Assets:
Available-for-sale securities		2,039,000	1,990,000
Fair Value, Measurements, Recurring | Foreign corporate bonds and other debt securities
Assets:
Available-for-sale securities		915,000	879,000
Fair Value, Measurements, Recurring | Equity securities (marketable)
Assets:
Available-for-sale securities	[1]		4,033,000
Fair Value, Measurements, Recurring | Level 1
Assets:
Equity securities with readily determinable fair values	[1]	4,413,000
Total assets measured at fair value		26,646,000	24,698,000
Liabilities:
Trading securities sold, not yet purchased		2,538,000	2,777,000
Total liabilities measured at fair value		2,706,000	2,915,000
Fair Value, Measurements, Recurring | Level 1 | Interest rate contracts
Assets:
Assets, derivatives		40,000	39,000
Liabilities:
Liabilities, derivatives		38,000	42,000
Fair Value, Measurements, Recurring | Level 1 | Foreign exchange contracts
Assets:
Assets, derivatives		16,000	17,000
Liabilities:
Liabilities, derivatives		16,000	11,000
Fair Value, Measurements, Recurring | Level 1 | Equity-related contracts
Assets:
Assets, derivatives		77,000	82,000
Liabilities:
Liabilities, derivatives		107,000	81,000
Fair Value, Measurements, Recurring | Level 1 | Other contracts
Assets:
Assets, derivatives		12,000	6,000
Liabilities:
Liabilities, derivatives		7,000	4,000
Fair Value, Measurements, Recurring | Level 1 | Japanese government bonds
Assets:
Assets, trading securities	[4]	1,935,000	1,375,000
Available-for-sale securities		12,444,000	12,435,000
Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury bonds and federal agency securities
Assets:
Assets, trading securities	[4]	2,664,000	2,442,000
Available-for-sale securities		1,134,000	686,000
Fair Value, Measurements, Recurring | Level 1 | Other foreign government bonds
Assets:
Assets, trading securities	[4]	1,705,000	1,682,000
Available-for-sale securities		451,000	355,000
Fair Value, Measurements, Recurring | Level 1 | Corporate bonds and other debt securities
Assets:
Assets, trading securities	[4]	31,000	25,000
Fair Value, Measurements, Recurring | Level 1 | Equity securities
Assets:
Assets, trading securities	[4]	1,724,000	1,642,000
Fair Value, Measurements, Recurring | Level 1 | Equity securities (marketable)
Assets:
Available-for-sale securities	[1]		3,912,000
Fair Value, Measurements, Recurring | Level 2
Assets:
Equity securities with readily determinable fair values	[1]	90,000
Total assets measured at fair value		19,012,000	20,703,000
Liabilities:
Trading securities sold, not yet purchased		268,000	618,000
Long-term debt	[3]	1,768,000	1,395,000
Total liabilities measured at fair value		8,752,000	11,552,000
Fair Value, Measurements, Recurring | Level 2 | Interest rate contracts
Assets:
Assets, derivatives		4,530,000	7,089,000
Liabilities:
Liabilities, derivatives		4,468,000	7,074,000
Fair Value, Measurements, Recurring | Level 2 | Foreign exchange contracts
Assets:
Assets, derivatives		2,323,000	2,667,000
Liabilities:
Liabilities, derivatives		2,115,000	2,370,000
Fair Value, Measurements, Recurring | Level 2 | Equity-related contracts
Assets:
Assets, derivatives		220,000	110,000
Liabilities:
Liabilities, derivatives		103,000	69,000
Fair Value, Measurements, Recurring | Level 2 | Credit-related contracts
Assets:
Assets, derivatives		20,000	16,000
Liabilities:
Liabilities, derivatives		20,000	20,000
Fair Value, Measurements, Recurring | Level 2 | Other contracts
Assets:
Assets, derivatives		8,000	8,000
Liabilities:
Liabilities, derivatives		10,000	6,000
Fair Value, Measurements, Recurring | Level 2 | Japanese government bonds
Assets:
Assets, trading securities	[4]	32,000	43,000
Available-for-sale securities		1,007,000	897,000
Fair Value, Measurements, Recurring | Level 2 | Japanese local government bonds
Assets:
Assets, trading securities	[4]	93,000	107,000
Available-for-sale securities		240,000	239,000
Fair Value, Measurements, Recurring | Level 2 | U.S. Treasury bonds and federal agency securities
Assets:
Assets, trading securities	[4]	193,000	209,000
Fair Value, Measurements, Recurring | Level 2 | Other foreign government bonds
Assets:
Assets, trading securities	[4]	492,000	480,000
Available-for-sale securities		792,000	703,000
Fair Value, Measurements, Recurring | Level 2 | Agency mortgage-backed securities
Assets:
Assets, trading securities	[4]	1,865,000	1,799,000
Available-for-sale securities		871,000	889,000
Fair Value, Measurements, Recurring | Level 2 | Residential mortgage-backed securities
Assets:
Available-for-sale securities		63,000	65,000
Fair Value, Measurements, Recurring | Level 2 | Certificates of deposit and commercial paper
Assets:
Assets, trading securities	[4]	1,322,000	643,000
Fair Value, Measurements, Recurring | Level 2 | Corporate bonds and other debt securities
Assets:
Assets, trading securities	[4]	2,198,000	1,992,000
Fair Value, Measurements, Recurring | Level 2 | Japanese corporate bonds and other debt securities
Assets:
Available-for-sale securities		1,883,000	1,827,000
Fair Value, Measurements, Recurring | Level 2 | Foreign corporate bonds and other debt securities
Assets:
Available-for-sale securities		770,000	799,000
Fair Value, Measurements, Recurring | Level 2 | Equity securities (marketable)
Assets:
Available-for-sale securities	[1]		121,000
Fair Value, Measurements, Recurring | Level 3
Assets:
Other investments		41,000	38,000
Total assets measured at fair value		2,117,000	1,901,000
Liabilities:
Trading securities sold, not yet purchased		2,000	4,000
Long-term debt	[3]	612,000	561,000
Total liabilities measured at fair value		666,000	604,000
Fair Value, Measurements, Recurring | Level 3 | Interest rate contracts
Assets:
Assets, derivatives		37,000	48,000
Liabilities:
Liabilities, derivatives		14,000	27,000
Fair Value, Measurements, Recurring | Level 3 | Foreign exchange contracts
Assets:
Assets, derivatives		28,000	13,000
Liabilities:
Liabilities, derivatives		3,000	1,000
Fair Value, Measurements, Recurring | Level 3 | Equity-related contracts
Assets:
Assets, derivatives		18,000	5,000
Liabilities:
Liabilities, derivatives		4,000	1,000
Fair Value, Measurements, Recurring | Level 3 | Credit-related contracts
Assets:
Assets, derivatives		2,000	2,000
Liabilities:
Liabilities, derivatives		2,000	1,000
Fair Value, Measurements, Recurring | Level 3 | Other contracts
Assets:
Assets, derivatives		29,000	9,000
Liabilities:
Liabilities, derivatives		29,000	9,000
Fair Value, Measurements, Recurring | Level 3 | Residential mortgage-backed securities
Assets:
Assets, trading securities	[4]	12,000	12,000
Available-for-sale securities		46,000	54,000
Fair Value, Measurements, Recurring | Level 3 | Commercial mortgage-backed securities
Assets:
Available-for-sale securities		469,000	441,000
Fair Value, Measurements, Recurring | Level 3 | Corporate bonds and other debt securities
Assets:
Assets, trading securities	[4]	1,105,000	1,013,000
Fair Value, Measurements, Recurring | Level 3 | Equity securities
Assets:
Assets, trading securities	[4]	29,000	23,000
Fair Value, Measurements, Recurring | Level 3 | Japanese corporate bonds and other debt securities
Assets:
Available-for-sale securities		156,000	163,000
Fair Value, Measurements, Recurring | Level 3 | Foreign corporate bonds and other debt securities
Assets:
Available-for-sale securities		¥ 145,000	¥ 80,000
[1]	The MHFG Group adopted ASU No.2016-01 on April 1, 2018. In connection with the adoption, equity securities are no longer classified as available-for-sale securities. See Note 2 "Recently issued accounting pronouncements" for further details.
[2]	In accordance with ASC 820, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented for these classes of assets are intended to permit the reconciliation of the fair value hierarchy to the amounts presented in the statements of financial position. The amounts of unfunded commitments related to these investments at March 31, 2018 and September 30, 2018 were ¥31 billion and ¥40 billion, respectively.
[3]	Amounts represent items for which the Group elected the fair value option or for which it applied the practicability exception.
[4]	Trading securities include foreign currency denominated securities for which the MHFG Group elected the fair value option.

Fair Value (Summary of Assets_2

Fair Value (Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis, Including Fair Value Option Elected) (Parenthetical) (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2018	Mar. 31, 2018
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unfunded commitments	¥ 40	¥ 31

Fair Value (Reconciliation for

Fair Value (Reconciliation for All Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Detail) - JPY (¥) ¥ in Billions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Credit Related Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		¥ 1
Gains (losses) in Earnings	[1]	(3)
Issuances		0
Settlements		2
Other investments
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		38	¥ 37
Gains (losses) in Earnings	[2]	1
Purchases		13	12
Issuances		0	0
Settlements		(11)	(10)
Ending Balance		41	39
Change in unrealized gain (losses) still held	[3]	2
Trading securities sold, not yet purchased
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		4
Gains (losses) in Earnings	[1]	1
Purchases		(30)	(57)
Sales		29	61
Ending Balance		2	4
Long-term debt
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers into Level 3		2
Beginning Balance		561	593
Gains (losses) in Earnings	[4]	2	(13)
Gains (losses) in OCI	[5]	3
Transfers into Level 3		2	1
Transfers out of level 3			(10)
Issuances		85	47
Settlements		(31)	(81)
Ending Balance		612	563
Change in unrealized gain (losses) still held	[3]	4	(14)
Trading securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers into Level 3			123
Transfers out of level 3			(240)
Trading securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		12	15
Issuances		0	0
Settlements			(1)
Ending Balance		12	14
Trading securities | Corporate bonds and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		1,013	1,052
Gains (losses) in Earnings	[1]	31	18	[6]
Transfers into Level 3			123
Transfers out of level 3			(240)
Purchases		457	562
Sales		(242)	(276)
Issuances		0	0
Settlements		(154)	(153)
Ending Balance		1,105	1,086
Change in unrealized gain (losses) still held	[3]	35	20
Trading securities | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		23	23
Gains (losses) in Earnings		2	(1)	[1]
Purchases		5
Sales		(1)
Issuances		0	0
Ending Balance		29	22
Change in unrealized gain (losses) still held	[3]		(1)
Derivative financial instruments assets | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		21	26	[7]
Gains (losses) in Earnings	[1]	1	(6)	[7]
Issuances		0	0	[7]
Settlements		1	1	[7]
Ending Balance		23	21	[7]
Change in unrealized gain (losses) still held	[3]	2	(6)	[7]
Derivative financial instruments assets | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		12	8	[7]
Gains (losses) in Earnings	[1]	15	(2)	[7]
Issuances		0	0	[7]
Settlements		(2)
Ending Balance		25	6	[7]
Change in unrealized gain (losses) still held	[3]	17	(2)	[7]
Derivative financial instruments assets | Equity-related contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		4	(25)	[7]
Gains (losses) in Earnings	[1]	(4)	(7)	[7]
Issuances		0	0	[7]
Settlements		14	6	[7]
Ending Balance		14	(26)	[7]
Change in unrealized gain (losses) still held	[3],[7]		(8)
Derivative financial instruments assets | Other contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Issuances	[7]		0
Settlements	[7]		1
Ending Balance	[7]		1
Available-for-sale securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers into Level 3		61	15
Transfers out of level 3			(29)
Available-for-sale securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		54	77
Purchases			1
Issuances		0	0
Settlements		(8)	(10)
Ending Balance		46	68
Available-for-sale securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		441	224
Purchases		57	40
Sales		(28)	(7)
Issuances		0	0
Settlements		(1)
Ending Balance		469	257
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		163	174
Gains (losses) in Earnings	[2]	10	(1)
Gains (losses) in OCI	[5]	(8)	(3)
Purchases		7	11
Sales		(7)
Issuances		0	0
Settlements		(9)	(16)
Ending Balance		156	165
Change in unrealized gain (losses) still held	[3]	10	(1)
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		80	110
Gains (losses) in OCI	[5]		1
Transfers into Level 3		61	15
Transfers out of level 3			(29)
Purchases		4
Issuances		0	0
Ending Balance		¥ 145	¥ 97
[1]	Gains (losses) in Earnings are reported in Trading account gains (losses)-net, Foreign exchange gains (losses)-net or Other noninterest income (expenses).
[2]	Gains (losses) in Earnings are reported in Investment gains (losses)-net.
[3]	Amounts represent total gains or losses recognized in earnings during the period. These gains or losses were attributable to the change in fair value relating to assets and liabilities classified as Level 3 that were still held at September 30, 2017 and 2018.
[4]	Gains (losses) in Earnings are reported in Other noninterest income (expenses).
[5]	Gains (losses) in OCI are reported in Other comprehensive income (loss).
[6]	In accordance with ASC 820, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented for these classes of assets are intended to permit the reconciliation of the fair value hierarchy to the amounts presented in the statements of financial position. The amounts of unfunded commitments related to these investments at March 31, 2018 and September 30, 2018 were ¥31 billion and ¥40 billion, respectively.
[7]	Total Level 3 derivative exposures have been netted on the table for presentation purposes only.

Fair Value (Quantitative Inform

Fair Value (Quantitative Information about Significant Unobservable Inputs Related to Material Classes of Level 3 Assets and Liabilities) (Detail) ¥ in Millions		Sep. 30, 2018JPY (¥)BasisPoint	Mar. 31, 2018JPY (¥)BasisPoint
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt | ¥		¥ 2,380,034	¥ 1,955,636
Available For Sale And Trading Securities | Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities | ¥		58,000	66,000
Available For Sale And Trading Securities | Commercial mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities | ¥		469,000	441,000
Available For Sale And Trading Securities | Corporate bonds and other debt securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities | ¥		1,406,000	1,256,000
Derivative Financial Instruments | Interest rate contracts
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments | ¥		23,000	21,000
Derivative Financial Instruments | Foreign exchange contracts
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments | ¥		25,000	12,000
Derivative Financial Instruments | Equity-related contracts
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments | ¥		14,000	4,000
Derivative Financial Instruments | Credit-related contracts
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments | ¥			1,000
Long-term debt
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt | ¥		¥ 612,000	¥ 561,000
Minimum | Measurement Input, Prepayment Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		0.04	0.03
Minimum | Measurement Input, Prepayment Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1]	0.27	0.26
Minimum | Measurement Input, Default Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		0	0
Minimum | Measurement Input, Default Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1]	0.02	0.01
Minimum | Measurement Input, Default Rate [Member] | Derivative Financial Instruments | Interest rate contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2],[3]	0	0
Minimum | Measurement Input, Default Rate [Member] | Derivative Financial Instruments | Foreign exchange contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2],[3]	0	0
Minimum | Measurement Input, Default Rate [Member] | Derivative Financial Instruments | Credit-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0	0
Minimum | Measurement Input, Default Rate [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0	0
Minimum | Measurement Input Recovery Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		1	1
Minimum | Measurement Input Recovery Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1]	0.69	0.60
Minimum | Measurement Input, Discount Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		15	17
Minimum | Measurement Input, Discount Rate [Member] | Available For Sale And Trading Securities | Commercial mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		9	9
Minimum | Measurement Input, Discount Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1]	93	12
Minimum | Measurement Input Discount Rate1 [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[4]	5	5
Minimum | Measurement Input, IR - IR correlation [Member] | Derivative Financial Instruments | Interest rate contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.23	0.23
Minimum | Measurement Input, IR - IR correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.23	0.23
Minimum | Measurement Input, FX - IR correlation [Member] | Derivative Financial Instruments | Foreign exchange contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.05	0.16
Minimum | Measurement Input, FX - IR correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.05	0.09
Minimum | Measurement Input, FX - FX correlation [Member] | Derivative Financial Instruments | Foreign exchange contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.64	0.61
Minimum | Measurement Input, FX - FX correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.64	0.61
Minimum | Measurement Input, Equity - IR correlation [Member] | Derivative Financial Instruments | Equity-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.25	0.25
Minimum | Measurement Input, Equity - IR correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.25	0.25
Minimum | Measurement Input, Equity - FX correlation [Member] | Derivative Financial Instruments | Equity-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.48
Minimum | Measurement Input, Equity - FX correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.55	0.55
Minimum | Measurement Input, Equity volatility [Member] | Derivative Financial Instruments | Equity-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.13	0.12
Minimum | Measurement Input, Equity volatility [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.14	0.13
Minimum | Measurement Input, Credit correlation [Member] | Derivative Financial Instruments | Credit-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.28	0.27
Minimum | Measurement Input, Credit correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.24	0.28
Minimum | Measurement Input, Equity correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.19	0.24
Maximum | Measurement Input, Prepayment Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		0.18	0.17
Maximum | Measurement Input, Prepayment Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1]	0.27	0.37
Maximum | Measurement Input, Default Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		0.01	0.01
Maximum | Measurement Input, Default Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1]	0.02	0.02
Maximum | Measurement Input, Default Rate [Member] | Derivative Financial Instruments | Interest rate contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2],[3]	0.63	0.63
Maximum | Measurement Input, Default Rate [Member] | Derivative Financial Instruments | Foreign exchange contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2],[3]	0.63	0.63
Maximum | Measurement Input, Default Rate [Member] | Derivative Financial Instruments | Credit-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.04	0.03
Maximum | Measurement Input, Default Rate [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.04	0.02
Maximum | Measurement Input Recovery Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		1	1
Maximum | Measurement Input Recovery Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1]	0.69	0.69
Maximum | Measurement Input, Discount Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		170	170
Maximum | Measurement Input, Discount Rate [Member] | Available For Sale And Trading Securities | Commercial mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities		198	141
Maximum | Measurement Input, Discount Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1]	1,194	1,165
Maximum | Measurement Input Discount Rate1 [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[4]	816	1,064
Maximum | Measurement Input, IR - IR correlation [Member] | Derivative Financial Instruments | Interest rate contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	1	1
Maximum | Measurement Input, IR - IR correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	1	1
Maximum | Measurement Input, FX - IR correlation [Member] | Derivative Financial Instruments | Foreign exchange contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.55	0.53
Maximum | Measurement Input, FX - IR correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.55	0.53
Maximum | Measurement Input, FX - FX correlation [Member] | Derivative Financial Instruments | Foreign exchange contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.64	0.61
Maximum | Measurement Input, FX - FX correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.64	0.61
Maximum | Measurement Input, Equity - IR correlation [Member] | Derivative Financial Instruments | Equity-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.25	0.25
Maximum | Measurement Input, Equity - IR correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.25	0.25
Maximum | Measurement Input, Equity - FX correlation [Member] | Derivative Financial Instruments | Equity-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	1
Maximum | Measurement Input, Equity - FX correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.70	0.70
Maximum | Measurement Input, Equity volatility [Member] | Derivative Financial Instruments | Equity-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	0.36	0.41
Maximum | Measurement Input, Equity volatility [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	0.59	0.56
Maximum | Measurement Input, Credit correlation [Member] | Derivative Financial Instruments | Credit-related contracts | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives financial instruments	[2]	1	1
Maximum | Measurement Input, Credit correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	1	1
Maximum | Measurement Input, Equity correlation [Member] | Long-term debt | Internal Valuation Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt	[2]	1	1
Weighted Average | Measurement Input, Prepayment Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[5]	0.07	0.07
Weighted Average | Measurement Input, Prepayment Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1],[5]	0.27	0.36
Weighted Average | Measurement Input, Default Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[5]	0	0
Weighted Average | Measurement Input, Default Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1],[5]	0.02	0.02
Weighted Average | Measurement Input Recovery Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[5]	1	1
Weighted Average | Measurement Input Recovery Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1],[5]	0.69	0.68
Weighted Average | Measurement Input, Discount Rate [Member] | Available For Sale And Trading Securities | Residential mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[5]	51	50
Weighted Average | Measurement Input, Discount Rate [Member] | Available For Sale And Trading Securities | Commercial mortgage-backed securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[5]	24	28
Weighted Average | Measurement Input, Discount Rate [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[1],[5]	122	115
Weighted Average | Measurement Input Discount Rate1 [Member] | Available For Sale And Trading Securities | Corporate bonds and other debt securities | Discounted Cash Flows Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading securities	[4],[5]	274	379
[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]	Internal valuation model includes discounted cash flow models and the Black-Scholes option pricing model.
[3]	This input represents the counterparty default rate derived from the MHFG Group's own internal credit analyses.
[4]	This input is mainly used for determining the fair values of Japanese corporate bonds and foreign corporate bonds.
[5]	Weighted averages are calculated by weighting each input by the relative fair value of the respective financial instruments.

Fair Value (Summary of Assets_3

Fair Value (Summary of Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis) (Detail) - JPY (¥) ¥ in Millions	Sep. 30, 2018	Mar. 31, 2018
Assets:
Equity securities	¥ 231,810
Fair Value, Measurements, Nonrecurring
Assets:
Loans	113,000	¥ 113,000
Loans held-for-sale		60,000
Equity securities	3,000	1,000
Other investments	5,000
Total assets measured at fair value	121,000	174,000
Fair Value, Measurements, Nonrecurring | Aggregate cost
Assets:
Loans	162,000	164,000
Loans held-for-sale		74,000
Equity securities	2,000	3,000
Other investments	7,000
Premises and equipment-net	2,000	4,000
Total assets measured at fair value	173,000	245,000
Fair Value, Measurements, Nonrecurring | Level 1
Assets:
Other investments	5,000
Total assets measured at fair value	5,000
Fair Value, Measurements, Nonrecurring | Level 2
Assets:
Loans held-for-sale		60,000
Total assets measured at fair value		60,000
Fair Value, Measurements, Nonrecurring | Level 3
Assets:
Loans	113,000	113,000
Equity securities	3,000	1,000
Total assets measured at fair value	¥ 116,000	¥ 114,000

Fair Value (Carrying Amounts an

Fair Value (Carrying Amounts and Fair Values of Certain Financial Instruments, Excluding Financial Instruments Carried at Fair Value on a Recurring Basis and Those outside Scope of ASC 825) (Detail) - JPY (¥) ¥ in Millions		Sep. 30, 2018	Mar. 31, 2018
Financial liabilities:
Long-term debt		¥ 2,380,034	¥ 1,955,636
Carrying amount
Financial assets:
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		60,425,000	61,381,000
Investments		2,137,000	2,518,000
Loans, net of allowance for loan losses	[1]	84,443,000	83,088,000
Financial liabilities:
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions		50,184,000	43,921,000
Interest-bearing deposits		108,932,000	113,558,000
Due to trust accounts		3,966,000	3,993,000
Other short-term borrowings		1,754,000	1,688,000
Long-term debt		11,151,000	10,970,000
Estimated fair value
Financial assets:
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		60,425,000	61,381,000
Investments		2,132,000	2,522,000
Loans, net of allowance for loan losses	[1]	85,403,000	84,041,000
Financial liabilities:
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions		50,184,000	43,921,000
Interest-bearing deposits		108,909,000	113,540,000
Due to trust accounts		3,966,000	3,993,000
Other short-term borrowings		1,754,000	1,688,000
Long-term debt		11,132,000	10,995,000
Estimated fair value | Level 1
Financial assets:
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		1,128,000	1,206,000
Investments		1,619,000	1,984,000
Financial liabilities:
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions		24,384,000	22,898,000
Interest-bearing deposits		55,443,000	61,719,000
Estimated fair value | Level 2
Financial assets:
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		59,297,000	60,175,000
Investments		513,000	538,000
Financial liabilities:
Noninterest-bearing deposits, call money and funds purchased, and payables under repurchase agreements and securities lending transactions		25,800,000	21,023,000
Interest-bearing deposits		53,466,000	51,821,000
Due to trust accounts		3,966,000	3,993,000
Other short-term borrowings		1,754,000	1,688,000
Long-term debt		10,264,000	10,098,000
Estimated fair value | Level 3
Financial assets:
Loans, net of allowance for loan losses	[1]	85,403,000	84,041,000
Financial liabilities:
Long-term debt		¥ 868,000	¥ 897,000
[1]	Loans, net of allowance for loan losses include items measured at fair value on a nonrecurring basis.

Offsetting of Financial Asset_3

Offsetting of Financial Assets and Financial Liabilities (Information of Offsetting of Financial Assets and Financial Liabilities) (Detail) - JPY (¥) ¥ in Billions		Sep. 30, 2018	Mar. 31, 2018
Offsetting Financial Assets And Financial Liabilities [Line Items]
Derivative assets, Gross amounts recognized	[1]	¥ 6,766	¥ 9,341
Derivative assets, Gross amounts offset on the balance sheet	[1]	0	0
Derivative assets, Net amounts presented on the balance sheet	[1],[2]	6,766	9,341
Derivative assets, Amounts not offset on the balance sheet, Financial instruments	[1],[3],[4]	(5,409)	(7,751)
Derivative assets, Amounts not offset on the balance sheet, Cash collateral	[1],[3]	(571)	(520)
Derivative assets, Net amounts	[1]	786	1,070
Receivables under resale agreements, Gross amounts recognized	[1]	10,144	7,804
Receivables under resale agreements, Gross amounts offset on the balance sheet	[1]	0	0
Receivables under resale agreements, Net amounts presented on the balance sheet	[1],[2]	10,144	7,804
Receivables under resale agreements, Amounts not offset on the balance sheet, Financial instruments	[1],[3],[4]	(10,075)	(7,763)
Receivables under resale agreements, Amounts not offset on the balance sheet, Cash collateral	[1],[3]	0	0
Receivables under resale agreements, Net amounts	[1]	69	41
Receivables under securities borrowing transactions, Gross amounts recognized	[1]	2,032	3,904
Receivables under securities borrowing transactions, Gross amounts offset on the balance sheet	[1]	0	0
Receivables under securities borrowing transactions, Net amounts presented on the balance sheet	[1],[2]	2,032	3,904
Receivables under securities borrowing transactions, Amounts not offset on the balance sheet, Financial instruments	[1],[3],[4]	(2,009)	(3,874)
Receivables under securities borrowing transactions, Amounts not offset on the balance sheet, Cash collateral	[1],[3]	0	0
Receivables under securities borrowing transactions, Net amounts	[1]	23	30
Financial assets, Gross amounts recognized, Total	[1]	18,942	21,049
Financial assets, Gross amounts offset on the balance sheet, Total	[1]	0	0
Financial assets, Net amounts presented on the balance sheet, Total	[1],[2]	18,942	21,049
Financial assets, Amounts not offset on the balance sheet, Financial instruments, Total	[1],[3],[4]	(17,493)	(19,388)
Financial assets, Amounts not offset on the balance sheet, Cash collateral, Total	[1],[3]	(571)	(520)
Financial assets, Net amounts, Total	[1]	878	1,141
Derivative liabilities, Gross amounts recognized	[1]	6,326	9,013
Derivative liabilities, Gross amounts offset on the balance sheet	[1]	0	0
Derivative liabilities, Net amounts presented on the balance sheet	[1],[2]	6,326	9,013
Derivative liabilities, Amounts not offset on the balance sheet, Financial instruments	[1],[3],[4]	(5,069)	(7,758)
Derivative liabilities, Amounts not offset on the balance sheet, Cash collateral	[1],[3]	(722)	(884)
Derivative liabilities, Net amounts	[1]	535	371
Payables under repurchase agreements, Gross amounts recognized	[1]	17,066	15,964
Payables under repurchase agreements, Gross amounts offset on the balance sheet	[1]	0	0
Payables under repurchase agreements, Net amounts presented on the balance sheet	[1],[2]	17,066	15,964
Payables under repurchase agreements, Amounts not offset on the balance sheet, Financial instruments	[1],[3],[4]	(17,045)	(15,847)
Payables under repurchase agreements, Amounts not offset on the balance sheet, Cash collateral	[1],[3]	0	0
Payables under repurchase agreements, Net amounts	[1]	21	117
Payables under securities lending transactions, Gross amounts recognized	[1]	1,359	1,181
Payables under securities lending transactions, Gross amounts offset on the balance sheet	[1]	0	0
Payables under securities lending transactions, Net amounts presented on the balance sheet	[1],[2]	1,359	1,181
Payables under securities lending transactions, Amounts not offset on the balance sheet, Financial instruments	[1],[3],[4]	(1,355)	(1,179)
Payables under securities lending transactions, Amounts not offset on the balance sheet, Cash collateral	[1],[3]	0	0
Payables under securities lending transactions, Net amounts	[1]	4	2
Financial liabilities, Gross amounts recognized, Total	[1]	24,751	26,158
Financial liabilities, Gross amounts offset on the balance sheet, Total	[1]	0	0
Financial liabilities, Net amounts presented on the balance sheet, Total	[1],[2]	24,751	26,158
Financial liabilities, Amounts not offset on the balance sheet, Financial instruments, Total	[1],[3],[4]	(23,469)	(24,784)
Financial liabilities, Amounts not offset on the balance sheet, Cash collateral, Total	[1],[3]	(722)	(884)
Financial liabilities, Net amounts, Total	[1]	¥ 560	¥ 490
[1]	Amounts relating to master netting arrangements or similar agreements where the MHFG 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.

Repurchase Agreements and Sec_3

Repurchase Agreements and Securities Lending Transactions Accounted for as Secured Borrowings (Gross Amounts of Liabilities by Remaining Contractual Maturity) (Detail) - JPY (¥) ¥ in Billions		Sep. 30, 2018	Mar. 31, 2018
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	[1]	¥ 17,488	¥ 16,657
Securities lending transactions	[1]	2,112	1,833
Total		19,600	18,490
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements		4,095	255
Securities lending transactions		1,068	1,270
Total		5,163	1,525
Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements		10,198	11,669
Securities lending transactions		771	355
Total		10,969	12,024
31 to 90 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements		1,687	3,676
Total		1,687	3,676
Greater than 90 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements		1,508	1,057
Securities lending transactions		273	208
Total		¥ 1,781	¥ 1,265
[1]	Amounts exceeded the gross amounts recognized in Note 18 "Offsetting of financial assets and financial liabilities" by ¥1,345 billion and ¥1,175 billion, at March 31, 2018 and September 30, 2018, respectively, which excluded the amounts relating to master netting agreements or similar agreements where the MHFG Group did not have the legal right of set-off or where uncertainty exists as to the enforceability.

Repurchase Agreements and Sec_4

Repurchase Agreements and Securities Lending Transactions Accounted for as Secured Borrowings (Gross Amounts of Liabilities by Class of Underlying Collateral) (Detail) - JPY (¥) ¥ in Billions		Sep. 30, 2018	Mar. 31, 2018
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	[1]	¥ 17,488	¥ 16,657
Securities lending transactions	[1]	2,112	1,833
Japanese government bonds and Japanese local government bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements		2,365	1,358
Securities lending transactions		320	592
Foreign government bonds and foreign agency mortgage-backed securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements		14,157	14,426
Securities lending transactions		700	303
Commercial Paper and Corporate Bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements		383	328
Securities lending transactions		51	48
Equity Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements		418	406
Securities lending transactions		1,021	869
Other securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements		165	139
Securities lending transactions		¥ 20	¥ 21
[1]	Amounts exceeded the gross amounts recognized in Note 18 "Offsetting of financial assets and financial liabilities" by ¥1,345 billion and ¥1,175 billion, at March 31, 2018 and September 30, 2018, respectively, which excluded the amounts relating to master netting agreements or similar agreements where the MHFG Group did not have the legal right of set-off or where uncertainty exists as to the enforceability.

Repurchase Agreements and Sec_5

Repurchase Agreements and Securities Lending Transactions Accounted for as Secured Borrowings (Gross Amounts of Liabilities by Class of Underlying Collateral) (Parenthetical) (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2018	Mar. 31, 2018
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Amounts exceeded the gross amounts recognized in offsetting of financial assets and financial liabilities	¥ 1,175	¥ 1,345

Business Segment Information -

Business Segment Information - Additional Information (Detail)	12 Months Ended
	Mar. 31, 2018Segment
Segment Reporting Information [Line Items]
Number of operating segments	5

Business Segment Information (R

Business Segment Information (Reportable Segment Information Derived from Internal Management Reporting Systems, on Basis of Japanese GAAP) (Detail) - JPY (¥) ¥ in Billions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits + Net gains (losses) related to ETFs and others		¥ 1,051.5	¥ 981.2
General and administrative expenses		(722.7)	711.3
Equity in earnings (losses) of equity method investees-net		19.4	10.6
Amortization of goodwill and others		6.8	7
Others		(10.4)	10.5
Net business profits (losses) + Net gains (losses) related to ETFs and others		331	263
Exchange Traded Funds
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits + Net gains (losses) related to ETFs and others		39.9	21.4
Operating Segments [Member] | Retail And Business Banking Company
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits + Net gains (losses) related to ETFs and others		345.9	343.2
General and administrative expenses		(360.2)	358.9
Equity in earnings (losses) of equity method investees-net		14.4	7.5
Amortization of goodwill and others		0.2	0.2
Net business profits (losses) + Net gains (losses) related to ETFs and others		(0.1)	(8.4)
Operating Segments [Member] | Corporate And Institutional Company
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits + Net gains (losses) related to ETFs and others		223.7	187.6
General and administrative expenses		(100.3)	101.3
Equity in earnings (losses) of equity method investees-net		0.6	0.6
Amortization of goodwill and others		0.2	0.2
Net business profits (losses) + Net gains (losses) related to ETFs and others		123.8	86.7
Operating Segments [Member] | Global Corporate Company
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits + Net gains (losses) related to ETFs and others		198.2	153.2
General and administrative expenses		(121.4)	121.6
Equity in earnings (losses) of equity method investees-net		2.8	1.3
Amortization of goodwill and others		0.2	0.2
Net business profits (losses) + Net gains (losses) related to ETFs and others		79.4	32.7
Operating Segments [Member] | Global Markets Company [Member]
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits + Net gains (losses) related to ETFs and others		237.4	239.9
General and administrative expenses		(103.5)	100.3
Amortization of goodwill and others		1.2	1.2
Net business profits (losses) + Net gains (losses) related to ETFs and others		132.7	138.4
Operating Segments [Member] | Asset Management Company
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits + Net gains (losses) related to ETFs and others		25	24.8
General and administrative expenses		(13.9)	13.9
Equity in earnings (losses) of equity method investees-net		0.6	0.5
Amortization of goodwill and others		4	4
Net business profits (losses) + Net gains (losses) related to ETFs and others		7.7	7.4
Others
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits + Net gains (losses) related to ETFs and others	[1]	21.3	32.5
General and administrative expenses	[1]	(23.4)	15.3
Equity in earnings (losses) of equity method investees-net	[1]	1	0.7
Amortization of goodwill and others	[1]	1	1.2
Others	[1]	(10.4)	10.5
Net business profits (losses) + Net gains (losses) related to ETFs and others	[1]	¥ (12.5)	¥ 6.2
[1]	"Others" includes items which should be eliminated as internal transactions between each segment on a consolidated basis.

Business Segment Information _2

Business Segment Information (Reportable Segment Information Derived from Internal Management Reporting Systems, on Basis of Japanese GAAP) (Parenthetical) (Detail) - JPY (¥) ¥ in Billions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits and net gains (losses) related to ETFs and others	¥ 1,051.5	¥ 981.2
Exchange Traded Funds
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits and net gains (losses) related to ETFs and others	39.9	21.4
Global Markets Company [Member] | Exchange Traded Funds
Japan Gaap Schedule of Segment Reporting Information, by Segment [Line Items]
Gross profits and net gains (losses) related to ETFs and others	¥ 33.6	¥ 13.9

Business Segment Information _3

Business Segment Information (Reconciliation of Total Net Business Profits under Internal Management Reporting Systems to Income Before Income Tax Expense on Consolidated Statements of Income) (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net business profits (losses) + Net gains (losses) related to ETFs and others		¥ 331,000	¥ 263,000
Less: Net gains (losses) related to ETFs and others		(1,051,500)	(981,200)
U.S. GAAP adjustments		(160,000)	95,700
(Provision) credit for loan losses		13,280	117,962
Net gains (losses) related to equity investments		289,500	100,900
Non-recurring personnel expense		900	(3,600)
Gains on disposal of premises and equipment	[1]	4,305	4,567
(Provision) credit for losses on off-balance-sheet instruments		9,877	4,191
Others-net		(31,400)	(48,500)
Income before income tax expense		417,650	512,863
Exchange Traded Funds
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Less: Net gains (losses) related to ETFs and others		¥ (39,900)	¥ (21,400)
[1]	These amounts are revenues from contracts that do not meet the scope of ASC 606.