Aetna 10-K 17 Feb 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Jan. 31, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Entity Registrant Name	AETNA INC /PA/
Entity Central Index Key	1,122,304
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		351.7
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 41,800

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 17,996	$ 2,524
Investments	3,046	3,015
Premiums receivable, net	2,356	1,880
Other receivables, net	2,224	2,307
Accrued investment income	232	228
Income taxes receivable	44	261
Other current assets	2,551	2,510
Total current assets	28,449	12,725
Long-term investments	21,833	21,665
Reinsurance recoverables	727	724
Goodwill	10,637	10,637
Other acquired intangible assets, net	1,442	1,688
Property and equipment, net	587	630
Other long-term assets	1,480	1,405
Separate Accounts Assets	3,991	4,035
Total assets	69,146	53,509
Current liabilities:
Health care costs payable	6,558	6,306
Future policy benefits	645	672
Unpaid claims	801	772
Unearned premiums	556	676
Policyholders' funds	2,772	2,263
Current portion of long-term debt	1,634	0
Accrued expenses and other current liabilities	5,728	4,920
Total current liabilities	18,694	15,609
Future policy benefits	5,929	6,268
Unpaid claims	1,703	1,656
Policyholders' funds	812	886
Long-term debt, less current portion	19,027	7,785
Deferred income taxes	4	177
Other long-term liabilities	1,043	914
Separate Accounts liabilities	3,991	4,035
Total liabilities	51,203	37,330
Commitments and contingencies (Note 17)
Shareholders' equity:
Common stock ($.01 par value; 2.5 billion shares authorized and 351.7 million shares issued and outstanding in 2016; 2.5 billion shares authorized and 349.5 million shares issued and outstanding in 2015) and additional paid-in capital	4,716	4,647
Retained earnings	14,717	12,797
Accumulated other comprehensive loss	(1,552)	(1,330)
Total Aetna shareholders' equity	17,881	16,114
Non-controlling interests	62	65
Total equity	17,943	16,179
Total liabilities and equity	$ 69,146	$ 53,509

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - $ / shares shares in Millions	Dec. 31, 2016	Dec. 31, 2015
Consolidated Balance Sheets (Parenthetical) [Abstract]
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	2,500	2,500
Common Stock, Shares, Issued	351.7	349.5
Common Stock, Shares, Outstanding	351.7	349.5

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue:
Health care premiums		$ 54,116	$ 51,618	$ 49,562
Other premiums		2,182	2,171	2,186
Fees and other revenue	[1]	5,861	5,696	5,229
Net investment income	[2]	910	917	946
Net realized capital gains (losses)		86	(65)	80
Total revenue		63,155	60,337	58,003
Benefits and expenses:
Health care costs	[3]	44,255	41,712	40,747
Current and future benefits		2,101	2,121	2,165
Operating expenses:
Selling expenses		1,678	1,611	1,653
General and administrative expenses		10,407	10,033	9,180
Total operating expenses		12,085	11,644	10,833
Interest expense	[2]	604	369	334
Amortization of other acquired intangible assets	[4]	247	255	243
Loss on early extinguishment of long-term debt	[4]	0	0	181
Reduction of reserve for anticipated future losses on discontinued products	[4]	(128)	0	0
Total benefits and expenses		59,164	56,101	54,503
Income before income taxes		3,991	4,236	3,500
Income taxes	[2]	1,735	1,841	1,455
Net income including non-controlling interests		2,256	2,395	2,045
Less: Net income (loss) attributable to non-controlling interests		(15)	5	4
Net income attributable to the Aetna	[4]	$ 2,271	$ 2,390	$ 2,041
Earnings per common share:
Basic		$ 6.46	$ 6.84	$ 5.74
Diluted		$ 6.41	$ 6.78	$ 5.68
Administrative Services Contract Member Co Payments And Plan Sponsor Reimbursements		$ 128	$ 112	$ 102
Pharmaceutical And Processing Costs		1,300	1,300	1,300
Insured Member Co Payments		$ 115	$ 117	$ 107
[1]	Fees and other revenue include administrative services contract member co-payments and plan sponsor reimbursements related to our mail order and specialty pharmacy operations of $128 million, $112 million and $102 million for 2016, 2015 and 2014, respectively (net of pharmaceutical and processing costs of $1.3 billion for each of 2016, 2015 and 2014).
[2]	Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer.
[3]	Health care costs have been reduced by Insured member co-payments related to our mail order and specialty pharmacy operations of $115 million, $117 million and $107 million for 2016, 2015 and 2014, respectively.
[4]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.

Statement of Comprehensive Inco

Statement of Comprehensive Income Statement - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income including non-controlling interests		$ 2,256	$ 2,395	$ 2,045
Other comprehensive income (loss)		(222)	(219)	(199)
Comprehensive income (loss) including non-controlling interests		2,034	2,176	1,846
Less: Comprehensive (loss) income attributable to non-controlling interests		(15)	5	4
Comprehensive income attributable to Aetna		2,049	2,171	1,842
Net Unrealized Gains (Losses) Previously Impaired Securities [Member]
Other comprehensive income (loss)	[1]	(3)	(16)	1
Net Unrealized Gains (Losses) All Other Securities [Member]
Other comprehensive income (loss)		(15)	(256)	241
Derivatives [Member]
Other comprehensive income (loss)		(161)	(13)	(61)
Pension and OPEB Plan [Member]
Other comprehensive income (loss)		$ (43)	$ 66	$ (380)
[1]	Represents specifically identified unrealized gains on the non-credit related component of impaired debt securities that we do not intend to sell and subsequent changes in the fair value of any previously impaired security.

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Total		Common Stock [Member]	Common Stock Including Additional Paid in Capital [Member]	Retained Earnings [Member]	Parent [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interest [Member]
Balance at beginning of period at Dec. 31, 2013				$ 4,382	$ 10,555	$ 14,025	$ (912)
Balance at beginning of period (in shares) at Dec. 31, 2013			362.2
Non-controlling interests at beginning of period at Dec. 31, 2013								$ 53
Total equity at beginning of period at Dec. 31, 2013	$ 14,078
Comprehensive income:
Net income attributable to the Aetna	2,041	[1]			2,041	2,041
Less: Net income (loss) attributable to non-controlling interests	4							4
Net income including non-controlling interests	2,045
Noncontrolling Interest, Period Increase (Decrease)	12			0		0		12
Other comprehensive income (loss) (Note 9):
Other comprehensive income (loss)	(199)					(199)	(199)
Other Comprehensive Income	1,842
Common shares issued for benefit plans, including tax benefits, net of employee tax withholdings	160			160		160
Common shares issued for benefit plans, including tax benefits, net of employee tax withholdings (in shares)			3.5
Repurchases of common shares	(1,218)			0	(1,218)	(1,218)
Repurchases of common shares (in shares)			(15.9)
Dividends declared	(326)				(326)	(326)
Balance at end of period at Dec. 31, 2014				4,542	11,052	14,483	(1,111)
Balance at end of period (in shares) at Dec. 31, 2014			349.8
Non-controlling interests at end of period at Dec. 31, 2014								69
Total equity at end of period at Dec. 31, 2014	14,552
Comprehensive income:
Net income attributable to the Aetna	2,390	[1]			2,390	2,390
Less: Net income (loss) attributable to non-controlling interests	5							5
Net income including non-controlling interests	2,395
Noncontrolling Interest, Period Increase (Decrease)	(9)			0		0		(9)
Other comprehensive income (loss) (Note 9):
Other comprehensive income (loss)	(219)					(219)	(219)
Other Comprehensive Income	2,171
Common shares issued for benefit plans, including tax benefits, net of employee tax withholdings	105			105		105
Common shares issued for benefit plans, including tax benefits, net of employee tax withholdings (in shares)			2.7
Repurchases of common shares	(296)			0	(296)	(296)
Repurchases of common shares (in shares)			(3)
Dividends declared	(349)				(349)	(349)
Balance at end of period at Dec. 31, 2015	$ 16,114			4,647	12,797	16,114	(1,330)
Balance at end of period (in shares) at Dec. 31, 2015	349.5		349.5
Non-controlling interests at end of period at Dec. 31, 2015	$ 65							65
Total equity at end of period at Dec. 31, 2015	16,179
Comprehensive income:
Net income attributable to the Aetna	2,271	[1]		0	2,271	2,271	0
Less: Net income (loss) attributable to non-controlling interests	(15)							(15)
Net income including non-controlling interests	2,256
Noncontrolling Interest, Period Increase (Decrease)	12			0		0		12
Other comprehensive income (loss) (Note 9):
Other comprehensive income (loss)	(222)					(222)	(222)
Other Comprehensive Income	2,049
Common shares issued for benefit plans, including tax benefits, net of employee tax withholdings	69			69		69
Common shares issued for benefit plans, including tax benefits, net of employee tax withholdings (in shares)			2.2
Dividends declared	(351)				(351)	(351)
Balance at end of period at Dec. 31, 2016	$ 17,881			$ 4,716	$ 14,717	$ 17,881	$ (1,552)
Balance at end of period (in shares) at Dec. 31, 2016	351.7		351.7
Non-controlling interests at end of period at Dec. 31, 2016	$ 62							$ 62
Total equity at end of period at Dec. 31, 2016	$ 17,943
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income including non-controlling interests		$ 2,256	$ 2,395	$ 2,045
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized capital losses (gains)		(86)	65	(80)
Depreciation and amortization		681	671	629
Debt fair value amortization		(30)	(30)	(53)
Amortization of Interest Rate Hedges		20	6	6
Equity in earnings of affiliates, net		(6)	(31)	(40)
Stock-based compensation expense		191	181	163
Reduction of reserve for anticipated future losses on discontinued products	[1]	(128)	0	0
Amortization of net investment premium		79	84	72
Loss on early extinguishment of long-term debt	[1]	0	0	181
Pension settlement charge	[1]	0	0	112
Changes in assets and liabilities:
Accrued investment income		(4)	(4)	(13)
Premiums due and other receivables		(153)	(616)	(784)
Income taxes		155	31	(154)
Other assets and other liabilities		653	644	363
Health care and insurance liabilities		91	470	926
Net cash provided by operating activities		3,719	3,866	3,373
Cash flows from investing activities:
Proceeds from sales and maturities of investments		14,741	12,299	9,484
Cost of investments		(14,852)	(12,943)	(10,804)
Additions to property, equipment and software		(270)	(363)	(370)
Cash used for acquisitions, net of cash acquired		0	(20)	(440)
Net cash provided by (used for) investing activities		(381)	(1,027)	(2,130)
Cash flows from financing activities:
Issuance of long-term debt		12,886	0	1,482
Repayment of long-term debt		0	(229)	(1,798)
Net (repayment) issuance of short-term debt		0	(500)	500
Deposits and interest credited to investment contracts net of (withdrawals)		1	(35)	2
Common shares issued under benefit plans, net		(139)	(143)	(60)
Stock-based compensation tax benefits		0	53	41
(Settlements) proceeds from repurchase agreements		0	(202)	202
Common shares repurchased		0	(296)	(1,218)
Dividends paid to shareholders		(351)	(349)	(321)
Net payment on interest rate derivatives		(274)	(25)	(77)
(Distributions) contributions, non-controlling interests		11	(9)	12
Net cash provided by (used for) financing activities		12,134	(1,735)	(1,235)
Net increase (decrease) in cash and cash equivalents		15,472	1,104	8
Cash and cash equivalents, beginning of period		2,524	1,420	1,412
Cash and cash equivalents, end of period		17,996	2,524	1,420
Interest Paid		541	338	379
Income Taxes Paid		$ 1,580	$ 1,755	$ 1,573
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.

Organization

Organization	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	1. Organization We conduct our operations in three business segments: • Health Care consists of medical, pharmacy benefit management services, dental, behavioral health and vision plans offered on both an Insured basis (where we assume all or a majority of the risk for medical and dental care costs) and an employer-funded basis (where the plan sponsor under an administrative services contract (“ASC”) assumes all or a majority of this risk) and emerging business products and services that complement and enhance our medical products. We also offer Medicare and Medicaid products and services and other medical products, such as medical management and data analytics services, medical stop loss insurance, workers’ compensation administrative services and products that provide access to our provider networks in select geographies. • Group Insurance primarily includes group life insurance and group disability products. Group life insurance products are offered on an Insured basis. Group disability products are offered to employers on both an Insured and an ASC basis. Group Insurance also includes long-term care products that were offered primarily on an Insured basis. We no longer solicit or accept new long-term care customers. • Large Case Pensions manages a variety of retirement products (including pension and annuity products) primarily for tax-qualified pension plans. These products provide a variety of funding and benefit payment distribution options and other services. Large Case Pensions also includes certain discontinued products (refer to Note 19 for additional information). Our three business segments are distinct businesses that offer different products and services. Our Chief Executive Officer evaluates financial performance and makes resource allocation decisions at these segment levels. The accounting policies of the segments are the same as those described in the summary of significant accounting policies in Note 2 . We evaluate the performance of these business segments based on operating earnings (net income or loss attributable to Aetna, excluding net realized capital gains or losses and other items, if any). Refer to Note 18 for segment financial information.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) and include the accounts of Aetna and the subsidiaries that we control. All significant intercompany balances have been eliminated in consolidation. The Company has evaluated subsequent events from the balance sheet date through the date the financial statements were issued and determined there were no subsequent events to disclose other than as disclosed in Notes 3, 9, 13, 16 and 17. Reclassifications Certain prior year amounts have been reclassified to conform to the current year presentation. Use of Estimates The preparation of the accompanying consolidated financial statements in conformity with GAAP requires the use of estimates and assumptions that affect the amounts reported in these consolidated financial statements and notes. We consider the following accounting estimates critical in the preparation of the accompanying consolidated financial statements: health care costs payable, other insurance liabilities, recoverability of goodwill and other acquired intangible assets, measurement of defined benefit pension and other postretirement employee benefit plans, other-than-temporary impairment of debt securities, revenue recognition, allowance for estimated terminations and uncollectible accounts and accounting for certain provisions of the Patient Protection and Affordable Care Act and the Health Care and Education Reconciliation Act of 2010 (as amended, collectively, the “ACA”). We use information available to us at the time estimates are made; however, these estimates could change materially if different information or assumptions were used. Additionally, these estimates may not ultimately reflect the actual amounts of the final transactions that occur. Cash and Cash Equivalents Cash and cash equivalents include cash on-hand and debt securities with an original maturity of three months or less when purchased. The carrying value of cash equivalents approximates fair value due to the short-term nature of these investments. Cash and cash equivalents at December 31, 2016 include approximately $13 billion of highly-rated money market fund investments related to the net proceeds received from the 2016 senior notes we issued in June 2016 to partially fund our then pending acquisition of Humana Inc. (the “Humana Acquisition”). These money market funds have average maturities of 60 days or less and are redeemable daily at par value plus accrued dividends with specified yield rates. Investments Debt and Equity Securities Debt and equity securities consist primarily of U.S. Treasury and agency securities, mortgage-backed securities, corporate and foreign bonds and other debt and equity securities. Debt securities are classified as either current or long-term investments based on their contractual maturities unless we intend to sell an investment within the next twelve months, in which case it is classified as current on our balance sheets. We have classified our debt and equity securities as available for sale and carry them at fair value. Refer to Note 5 for additional information on how we estimate the fair value of these investments. The cost for mortgage-backed and other asset-backed securities is adjusted for unamortized premiums and discounts, which are amortized using the interest method over the estimated remaining term of the securities, adjusted for anticipated prepayments. We regularly review our debt and equity securities to determine whether a decline in fair value below the carrying value is other-than-temporary. When a debt or equity security is in an unrealized capital loss position, we monitor the duration and severity of the loss to determine if sufficient market recovery can occur within a reasonable period of time. If a decline in the fair value of a debt security is considered other-than-temporary, the cost basis or carrying value of the debt security is written down. The write-down is then bifurcated into its credit and non-credit related components. The amount of the credit-related component is included in our operating results, and the amount of the non-credit related component is included in other comprehensive income, unless we intend to sell the debt security or it is more likely than not that we will be required to sell the debt security prior to its anticipated recovery of its amortized cost basis. We do not accrue interest on debt securities when management believes the collection of interest is unlikely. If we intend to sell an equity security, we will recognize the unrealized capital gain or loss in our operating results. Mortgage Loans We value our mortgage loan investments on our balance sheet at the unpaid principal balance, net of impairment reserves. A mortgage loan may be impaired when it is a problem loan (i.e., more than 60 days delinquent, in bankruptcy or in process of foreclosure), a potential problem loan (i.e., high probability of default) or a restructured loan. For impaired loans, a specific impairment reserve is established for the difference between the recorded investment in the loan and the estimated fair value of the collateral. We apply our loan impairment policy individually to all loans in our portfolio. The impairment evaluation described above also considers characteristics and risk factors attributable to the aggregate portfolio. We establish an additional allowance for loan losses if it is probable that there will be a credit loss on a group of similar mortgage loans. We consider the following characteristics and risk factors when evaluating if a credit loss is probable on a group of similar mortgage loans: loan to value ratios, property type (e.g., office, retail, apartment, industrial), geographic location, vacancy rates and property condition. As a result of that evaluation, we determined that a credit loss was not probable and did not record any additional allowance for groups of similar mortgage loans in 2016 , 2015 or 2014 . We record full or partial impairments of loans at the time an event occurs affecting the legal status of the loan, typically at the time of foreclosure or upon a loan modification giving rise to forgiveness of debt. Interest income on a potential problem loan or restructured loan is accrued to the extent we deem it collectible and the loan continues to perform under its original or restructured terms. Interest income on problem loans is recognized on a cash basis. Cash payments on loans in the process of foreclosure are treated as a return of principal. Mortgage loans with a maturity date or a committed prepayment date within twelve months are classified as current on our balance sheets. Other Investments Other investments consist primarily of the following: • Private equity and hedge fund limited partnerships, which are carried at fair value on our balance sheets. The fair values of private equity limited partnerships are estimated based on the fair value of the underlying investment funds provided by the general partner or manager of the investments, the financial statements of which generally are audited. We typically do not have a controlling ownership in our private equity limited partnership investments, and therefore we apply the equity method of accounting for these investments. Hedge fund limited partnerships are carried at fair value which is estimated using the net asset value (“NAV”) per unit as reported by the administrator of the underlying investment fund as a practical expedient to fair value. We review our investments for impairment at least quarterly and monitor their performance throughout the year through discussions with the administrators, managers and/or general partners. If we become aware of an impairment of a limited partnership's investments through our review or prior to receiving the limited partnership's financial statements at the balance sheet date, we will recognize an impairment by recording a reduction in the carrying value of the limited partnership with a corresponding charge to realized capital losses. • Investment real estate, which is carried on our balance sheets at depreciated cost, including capital additions, net of write-downs for other-than-temporary declines in fair value. Depreciation is calculated using the straight-line method based on the estimated useful life of each asset. If any of our real estate investments is considered held-for-sale, we carry it at the lower of its carrying value or fair value less estimated selling costs. We generally estimate fair value using a discounted future cash flow analysis in conjunction with comparable sales information. At the time of the sale, we record the difference between the sales price and the carrying value as a realized capital gain or loss. • Privately-placed equity securities, which are carried at cost on our balance sheets. We do not estimate the fair value of these securities if there are no identified events or changes in circumstances that may have a significant adverse effect on the fair value of the investment. Additionally, as a member of the Federal Home Loan Bank of Boston (“FHLBB”), we are required to purchase and hold shares of the FHLBB. These shares are restricted and also carried at cost. • Bank loans, which are carried on our balance sheets at amortized cost, net of any allowance for impairments. If any of our bank loans are considered held-for-sale, we carry those loans at the lower of cost or fair value. • Derivatives, which we make limited use of in order to manage interest rate, foreign exchange and price risk and credit exposure. The derivatives we use consist primarily of interest rate swaps, treasury rate locks, forward contracts, futures contracts, warrants, put options, and credit default swaps. Derivative assets are recorded in investments and derivative liabilities are recorded in accrued expenses and other current liabilities on our balance sheets and reflected at fair value. When we enter into a derivative contract, if certain criteria are met, we may designate it as one of the following: a hedge of the fair value of a recognized asset or liability or of an unrecognized firm commitment; a hedge of a forecasted transaction or of the variability of cash flows to be received or paid related to a recognized asset or liability; or a foreign currency fair value or cash flow hedge. Net Investment Income Net investment income on investments supporting Health Care and Group Insurance liabilities and Large Case Pensions products (other than experience-rated and discontinued products) is reflected in our operating results. Experience-rated products are products in the Large Case Pensions business where the contract holder, not us, assumes investment and other risks, subject to, among other things, minimum guarantees provided by us. The effect of investment performance on experience-rated products is allocated to contract holders’ accounts daily, based on the underlying investment experience and, therefore, does not impact our operating results (as long as our minimum guarantees are not triggered). When we discontinued the sale of our fully-guaranteed Large Case Pensions products, we established a reserve for anticipated future losses from these discontinued products and segregated the related investments. Investment performance on this separate portfolio is ultimately credited/charged to the reserve and, generally, does not impact our operating results. Net investment income supporting Large Case Pensions’ experience-rated and discontinued products is included in net investment income in our statements of income and is credited to contract holders’ accounts or the reserve for anticipated future losses through a charge to current and future benefits. Realized/Unrealized Capital Gains and Losses Realized capital gains and losses on investments supporting Health Care and Group Insurance liabilities and Large Case Pensions products (other than experience-rated and discontinued products) are reflected in our operating results. Realized capital gains and losses are determined on a specific identification basis. We reflect purchases and sales of debt and equity securities and alternative investments on the trade date. We reflect purchases and sales of mortgage loans and investment real estate on the closing date. Realized capital gains and losses on investments supporting Large Case Pensions’ experience-rated and discontinued products are not included in realized capital gains and losses in our statements of income and instead are credited directly to contract holders’ accounts, in the case of experience-rated products, or allocated to the reserve for anticipated future losses, in the case of discontinued products. The contract holders’ accounts are reflected in policyholders’ funds, and the reserve for anticipated future losses is reflected in future policy benefits on our balance sheets. Unrealized capital gains and losses on investments supporting Health Care and Group Insurance liabilities and Large Case Pensions products (other than experience-rated and discontinued products) are reflected in shareholders’ equity, net of tax, as a component of accumulated other comprehensive loss. Unrealized capital gains and losses on investments supporting Large Case Pensions’ experience-rated products are credited directly to contract holders’ accounts, which are reflected in policyholders’ funds on our balance sheets. Unrealized capital gains and losses on discontinued products are reflected in other long-term liabilities on our balance sheets. Refer to Note 19 for additional information on our discontinued products. Premium Receivables Premium receivables include the uncollected amounts from fully-insured groups, individuals and government programs and are reported net of an allowance for estimated terminations and uncollectible accounts of $139 million and $146 million at December 31, 2016 and 2015, respectively. We estimate the allowance for estimated terminations and uncollectible accounts using management’s best estimate of collectability, taking into consideration the age of the outstanding amount, historical collection patterns and other economic factors. Other Receivables Other receivables include uncollected amounts from self-funded groups, pharmacy rebates, other government receivables, proceeds due from brokers on investment trades, provider advances and other miscellaneous amounts due to us. These receivables are reported net of an allowance for uncollectible accounts of $37 million and $20 million at December 31, 2016 and 2015, respectively. We estimate the allowance for uncollectible accounts using management’s best estimate of collectability, taking into consideration the age of the outstanding amount, historical collection patterns and other economic factors. Reinsurance Recoverables We utilize reinsurance agreements primarily to reduce our required capital and to facilitate the acquisition or disposition of certain insurance contracts. Ceded reinsurance agreements permit us to recover a portion of our losses from reinsurers, although they do not discharge our primary liability as the direct insurer of the risks reinsured. Failure of reinsurers to indemnify us could result in losses; however, we do not expect charges for unrecoverable reinsurance to have a material effect on our operating results or financial position. We evaluate the financial condition of our reinsurers and monitor concentrations of credit risk arising from similar geographic regions, activities or economic characteristics of our reinsurers. At December 31, 2016 , our reinsurance recoverables consisted primarily of amounts due from third parties that are rated consistent with companies that are considered to have the ability to meet their obligations. Health Care Contract Acquisition Costs Health care benefits products included in our Health Care segment are cancelable by either the customer or the member monthly upon written notice. Acquisition costs related to our prepaid health care and health indemnity contracts are generally expensed as incurred. At December 31, 2016 and 2015 , the balance of our deferred acquisition costs was $412 million and $305 million , respectively, comprised primarily of commissions paid on our Medicare Supplement products. Deferred acquisition costs are recorded as other current assets or other long-term assets on our balance sheets and are amortized over the estimated life of the contracts. Goodwill and Other Acquired Intangible Assets When we complete an acquisition, we apply the acquisition method of accounting, which requires the recognition of goodwill (the excess cost of the acquisition over the fair value of net assets acquired and identified intangible assets). We evaluate goodwill for impairment (at the reporting unit level) annually, or more frequently if circumstances indicate a possible impairment, by comparing an estimate of the fair value of the applicable reporting unit to its carrying value, including goodwill. If the carrying value exceeds fair value, we have historically compared the implied fair value of the applicable goodwill to its carrying amount to measure the amount of goodwill impairment, if any. Beginning in 2017, we adopted, on a prospective basis, the recently issued accounting standards update related to the methodology utilized to evaluate goodwill impairment. This update simplifies the methodology used to perform our annual, or interim, goodwill impairment evaluations. Our evaluation will be performed by comparing the estimated fair value of a reporting unit with its carrying amount. An impairment charge would be recognized when the carrying amount exceeds the estimated fair value of the reporting unit. Impairments, if any, would be classified as an operating expense. The fair value of each reporting unit substantially exceeded its carrying value in each of the years in the three-year period ended December 31, 2016 , and therefore there were no goodwill impairment losses recognized in any of those years. Our annual impairment tests were based on an evaluation of future discounted cash flows. These evaluations utilized the best information available to us at the time, including supportable assumptions and projections we believe are reasonable. Collectively, these evaluations were our best estimates of projected future cash flows. Our discounted cash flow evaluations used discount rates that correspond to a weighted-average cost of capital consistent with a market-participant view. The discount rates are consistent with those used for investment decisions and take into account the operating plans and strategies of the Health Care and Group Insurance segments. Certain other key assumptions utilized, including changes in membership, revenue, health care costs, operating expenses, impacts of health care reform fees, assessments and taxes, and effective tax rates, are based on estimates consistent with those utilized in our annual planning process that we believe are reasonable. If we do not achieve our earnings objectives, the assumptions and estimates underlying these goodwill impairment evaluations could be adversely affected, and we may impair a portion of our goodwill, which would adversely affect our operating results in the period of impairment. We report other acquired intangible assets at historical cost, net of accumulated amortization. Other acquired intangible assets primarily relate to provider networks, customer lists, value of business acquired (“VOBA”), technology and trademarks and are amortized over the useful-life based upon the pattern of future cash flows attributable to the asset. Other than VOBA and indefinite lived trademarks, other acquired intangible assets generally are amortized using the straight-line method. VOBA is amortized over the expected life of the acquired contracts in proportion to estimated premiums. Other intangible assets with indefinite lives are not amortized but are tested for impairment at least annually. We regularly evaluate whether events or changes in circumstances indicate that the carrying value of other acquired intangible assets may not be recoverable. If we determine that the carrying value of an asset may not be recoverable, we group the asset with other assets and liabilities at the lowest level for which independent identifiable cash flows are available and estimate the future undiscounted cash flows expected to result from future use of the asset group and its eventual disposition. If the sum of the expected undiscounted future cash flows is less than the carrying value of the asset group, we recognize an impairment loss for the amount by which the carrying value of the asset group exceeds its fair value. There were no material impairment losses on other acquired intangible assets recognized in any of the three years ended December 31, 2016 , 2015 or 2014 . Property and Equipment We report property and equipment at historical cost, net of accumulated depreciation. At December 31, 2016 and 2015 , the historical cost of property and equipment was each approximately $1.4 billion , and the related accumulated depreciation was $851 million and $774 million , respectively. We calculate depreciation primarily using the straight-line method over the estimated useful lives of the respective assets, which range from 10 to 40 years for buildings and 3 to 15 years for equipment. Depreciation expense was $125 million , $131 million and $137 million for the years ended December 31, 2016, 2015 and 2014, respectively. If we determine the carrying value of our property and equipment is not recoverable, an impairment charge is recorded. There were no material impairment losses on property and equipment recognized in any of the three years ended December 31, 2016, 2015 or 2014. Separate Accounts Separate Accounts assets and liabilities in the Large Case Pensions segment represent funds maintained to meet specific objectives of contract holders who bear the investment risk. These assets and liabilities are carried at fair value. Net investment income and net realized capital gains and losses accrue directly to such contract holders. The assets of each account are legally segregated and are not subject to claims arising from our other businesses. Deposits, withdrawals, net investment income and net realized and net unrealized capital gains and losses on Separate Accounts assets are not reflected in our statements of income or cash flows. Management fees charged to contract holders are included in fees and other revenue and recognized over the period earned. Health Care Costs Payable Health care costs payable consist principally of unpaid fee-for-service medical, dental and pharmacy claims, capitation costs and other amounts due to health care providers pursuant to risk-sharing arrangements related to the Health Care segment’s Insured Commercial, Medicare and Medicaid products. Unpaid health care claims include our estimate of payments we will make on claims reported to us but not yet paid and for services rendered to members but not yet reported to us as of the balance sheet date (collectively, “IBNR”) in our Health Care segment. Also included in these estimates is the cost of services that will continue to be rendered after the balance sheet date if we are obligated to pay for such services in accordance with contractual or regulatory requirements. Such estimates are developed using actuarial principles and assumptions which consider, among other things, historical and projected claim submission and processing patterns, assumed and historical medical cost trends, historical utilization of medical services, claim inventory levels, changes in membership and product mix, seasonality and other relevant factors. We reflect changes in these estimates in health care costs in our operating results in the period they are determined. Capitation costs represent contractual monthly fees paid to participating physicians and other medical providers for providing medical care, regardless of the medical services provided to the member. Approximately 4% , 4% and 5% of our health care costs related to capitated arrangements in 2016, 2015 and 2014, respectively. Amounts due under risk-sharing arrangements are based on the terms of the underlying contracts with the providers and consider claims experience under the contracts through the balance sheet date. We develop our estimate of IBNR using actuarial principles and assumptions that consider numerous factors. Of those factors, we consider the analysis of historical and projected claim payment patterns (including claims submission and processing patterns) and the assumed health care cost trend rate (the year-over-year change in per member per month health care costs) to be the most critical assumptions. In developing our estimate of IBNR, we consistently apply these actuarial principles and assumptions each period, with consideration to the variability of related factors. There have been no significant changes to the methodologies or assumptions used to calculate IBNR in 2016. We analyze historical claim payment patterns by comparing claim incurred dates (i.e., the date services were provided) to claim payment dates to estimate “completion factors.” We estimate completion factors by aggregating claim data based on the month of service and month of claim payment and estimating the percentage of claims incurred for a given month that are complete by each month thereafter. For any given month, substantially all claims are paid within six months of the date of service, but it can take up to 48 months or longer before all of the claims are completely resolved and paid. These historically-derived completion factors are then applied to claims paid through the financial statement date to estimate the ultimate claim cost for a given month’s incurred claim activity. The difference between the estimated ultimate claim cost and the claims paid through the financial statement date represents our estimate of claims remaining to be paid as of the financial statement date and is included in our health care costs payable. We use completion factors predominantly to estimate reserves for claims with claim incurred dates greater than three months prior to the financial statement date. The completion factors we use reflect judgments and possible adjustments based on data such as claim inventory levels, claim submission and processing patterns and, to a lesser extent, other factors such as changes in health care cost trend rates, changes in membership and changes in product mix. If claims are submitted or processed on a faster (slower) pace than prior periods, the actual claims may be more (less) complete than originally estimated using our completion factors, which may result in reserves that are higher (lower) than the ultimate cost of claims. Because claims incurred within three months prior to the financial statement date are less mature, we use a combination of historically-derived completion factors and the assumed health care cost trend rate to estimate the ultimate cost of claims incurred for these months. We place a greater emphasis on the assumed health care cost trend rate for the most recent claim incurred dates as these months may be influenced by seasonal patterns and changes in membership and product mix. Our health care cost trend rate is affected by changes in per member utilization of medical services as well as changes in the unit cost of such services. Many factors influence the health care cost trend rate, including our ability to manage health care costs through product design, negotiation of favorable provider contracts and medical management programs, as well as the mix of our business. The health status of our members, aging of the population and other demographic characteristics, advances in medical technology and other factors continue to contribute to rising per member utilization and unit costs. Changes in health care practices, inflation, new technologies, increases in the cost of prescription drugs (including specialty pharmacy drugs), direct-to-consumer marketing by pharmaceutical companies, clusters of high-cost cases, claim intensity, changes in the regulatory environment, health care provider or member fraud and numerous other factors also contribute to the cost of health care and our health care cost trend rate. For each reporting period, we use an extensive degree of judgment in the process of estimating our health care costs payable. As a result, considerable variability and uncertainty is inherent in such estimates; and the adequacy of such estimates is highly sensitive to changes in assumed completion factors and the assumed health care cost trend rates. For each reporting period we recognize the actuarial best estimate of health care costs payable considering the potential volatility in assumed completion factors and health care cost trend rates, as well as other factors. We believe our estimate of health care costs payable is reasonable and adequate to cover our obligations at December 31, 2016; however, actual claim payments may differ from our estimates. A worsening (or improvement) of our health care cost trend rates or changes in completion factors from those that we assumed in estimating health care costs payable at December 31, 2016 would cause these estimates to change in the near term, and such a change could be material. Each quarter, we re-examine previously established health care costs payable estimates based on actual claim payments for prior periods and other changes in facts and circumstances. Given the extensive degree of judgment in this estimate, it is possible that our estimates of health care costs payable could develop either favorably (that is, our actual health care costs for the period were less than we estimated) or unfavorably. The changes in our estimate of health care costs payable may relate to a prior quarter, prior year or earlier periods. For our roll forward of our health care costs payable, refer to Note 7 . Our reserving practice is to consistently recognize the actuarial best estimate of our ultimate liability for health care costs payable. Unpaid claims Unpaid claims consist primarily of reserves associated with certain short-duration group disability and term life insurance contracts in the Group Insurance segment, including an estimate for IBNR in our Group Insurance segment as of the balance sheet date. Reserves associated with certain short-duration group disability and term life insurance contracts are based upon our estimate of the present value of future benefits, which is based on assumed investment yields and assumptions regarding mortality, morbidity and recoveries from the U.S. Social Security Administration. We develop our estimate of IBNR using actuarial principles and assumptions which consider, among other things, contractual requirements, claim incidence rates, claim recovery rates, seasonality and other relevant factors. We discount certain claim liabilities related to group long-term disability and life insurance waiver of premium contracts. The discount rates generally reflect our expected investment returns for the investments supporting all incurral years of these liabilities. The discount rates for retrospectively-rated contracts are set at contractually specified levels. Our estimates of unpaid claims are subject to change due to changes in the underlying experience of the insurance contracts, changes in investment yields or other factors, and these changes are recorded in current and future benefits in our statements of income in the period they are determined. Refer to Note 7 for additional information related to our long-term disability unpaid claim liabilities. We estimate our reserve for claims IBNR for life products largely based on completion factors. The completion factors we use are based on our historical experience and reflect judgments and possible adjustments based on data such as claim inventory levels, claim payment patterns, changes in business volume and other factors. If claims are submitted or processed on a faster (slower) pace than historical periods, the actual claims may be more (less) complete than originally estimated using our completion factors, which may result in reserves that are higher (lower) than required to cover future life benefit payments. At December 31, 2016, we held $246 million in reserves for life claims incurred but not yet reported to us. There have been no significant changes to the methodologies or assumptions

Acquisitions, Terminated Acquis

Acquisitions, Terminated Acquisition and Terminated Divestiture	12 Months Ended
	Dec. 31, 2016
Business Combinations [Abstract]
Acquisitions	3. Acquisitions, Terminated Acquisition and Terminated Divestiture Terminated Acquisition of Humana and Terminated Divestiture to Molina On July 2, 2015, we entered into a definitive agreement (the “Merger Agreement”) to acquire Humana Inc. (“Humana”) in a transaction valued at approximately $37.0 billion , based on the closing price of Aetna common shares on July 2, 2015, including the assumption of Humana debt and Humana cash and cash equivalents. On July 21, 2016, the U.S. Department of Justice (the “DOJ”) and certain state attorneys general filed a civil complaint in the U.S. District Court for the District of Columbia (the “District Court”) against us and Humana charging that the Humana Acquisition would violate Section 7 of the Clayton Antitrust Act, and seeking a permanent injunction to prevent Aetna from acquiring Humana. On January 23, 2017, the District Court granted the DOJ’s request to enjoin the Humana Acquisition. On February 14, 2017, Aetna and Humana entered into a mutual termination agreement (the “Termination Agreement”) pursuant to which the parties thereto (collectively the “Parties”) agreed to terminate the Merger Agreement, including all schedules and exhibits thereto, and all ancillary agreements contemplated thereby, entered pursuant thereto or entered in connection therewith (other than certain confidentiality agreements) (collectively with the Merger Agreement, the “Transaction Documents”), effective immediately as of February 14, 2017 (the “Termination Date”). Under the Termination Agreement, Aetna agreed to pay Humana the Regulatory Termination Fee (as defined in the Merger Agreement) of $1.0 billion in cash in full satisfaction of any amounts required to be paid by Aetna under the Merger Agreement. The Parties also agreed to release each other from any and all liability, claims, rights, actions, causes of action, suits, liens, obligations, accounts, debts, demands, agreements, promises, liabilities, controversies, costs, charges, damages, expenses and fees, however arising, in connection with, arising out of or related to the Transaction Documents, the transactions contemplated therein or thereby or certain related matters. We paid Humana the Regulatory Termination Fee on February 16, 2017 and funded that payment with the proceeds of the 2016 senior notes (as defined below). In June 2016, we issued $13.0 billion of senior notes to partially fund the Humana Acquisition (collectively, the “2016 senior notes”). In accordance with the terms of the 2016 senior notes, on February 14, 2017, we issued a notice of redemption for $10.2 billion aggregate principal amount of certain of the 2016 senior notes (collectively, the “Special Mandatory Redemption Notes”) at a redemption price equal to 101% of the aggregate principal amount of those notes plus accrued and unpaid interest. We will redeem the Special Mandatory Redemption Notes on or about March 16, 2017. As a result of the redemption of the Special Mandatory Redemption Notes, in the first quarter of 2017, we will recognize on a pretax basis in our net income the entire approximately $420 million unamortized portion of the related cash flow hedge losses, debt issuance costs and debt issuance discounts and the entire approximately $100 million redemption premium paid on the Special Mandatory Redemption Notes upon such redemption. In order to address the DOJ’s perceived competitive concerns regarding Medicare Advantage relating to the Humana Acquisition, on August 2, 2016, we entered into a definitive agreement (the “Aetna APA”) to sell for cash to Molina Healthcare, Inc. (“Molina”) certain of our Medicare Advantage assets. On February 14, 2017, Aetna and Molina entered into a Termination Agreement (the “APA Termination Agreement”) pursuant to which Aetna terminated the Molina APA, including all schedules and exhibits thereto, and all ancillary agreements contemplated thereby or entered pursuant thereto. Under the APA Termination Agreement, Aetna agreed to pay Molina in cash (a) a termination fee of $53 million and (b) approximately 70% of Molina’s transaction costs. We paid Molina the termination fee on February 16, 2017 and funded that payment with the proceeds of the 2016 senior notes. We expect to pay Molina the applicable transaction costs during the first quarter of 2017. Acquisition of bswift LLC In November 2014, we acquired bswift LLC (“bswift”) for approximately $400 million . bswift provides a technology platform that offers a retail shopping experience for health insurance exchanges and employees nationwide, and provides benefit administration technology and services to employers. We recorded goodwill related to this transaction of $329 million , none of which will be tax deductible. All of the goodwill related to this acquisition was assigned to our Health Care segment. Acquisition of the InterGlobal Group In April 2014, we acquired the InterGlobal group (“InterGlobal”), a company that specializes in international private medical insurance for groups and individuals in the Middle East, Asia, Africa and Europe. The purchase price was not material, and the goodwill related to this acquisition was assigned to our Health Care segment.

Investments

Investments	12 Months Ended
	Dec. 31, 2016
Investments [Abstract]
Investments	4. Investments Total investments at December 31, 2016 and 2015 were as follows: 2016 2015 (Millions) Current Long-term Total Current Long-term Total Debt and equity securities available for sale $ 2,876 $ 18,866 $ 21,742 $ 2,877 $ 18,446 $ 21,323 Mortgage loans 170 1,341 1,511 127 1,427 1,554 Other investments — 1,626 1,626 11 1,792 1,803 Total investments $ 3,046 $ 21,833 $ 24,879 $ 3,015 $ 21,665 $ 24,680 At December 31, 2016 and 2015 , we held investments of $657 million and $690 million , respectively, related to the 2012 conversion of an existing group annuity contract from a participating to a non-participating contract. These investments are included in the total investments of our Large Case Pensions segment supporting non-experience-rated products. Although these investments are not accounted for as Separate Accounts assets, they are legally segregated and are not subject to claims that arise out of our business and only support our future policy benefits obligations under that group annuity contract. Refer to Note 2 for additional information. Debt and Equity Securities Debt and equity securities available for sale at December 31, 2016 and 2015 were as follows: (Millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value December 31, 2016 Debt securities: U.S. government securities $ 1,643 $ 51 $ — $ 1,694 States, municipalities and political subdivisions 5,047 152 (61 ) 5,138 U.S. corporate securities 8,145 385 (55 ) 8,475 Foreign securities 2,958 163 (33 ) 3,088 Residential mortgage-backed securities 793 11 (9 ) 795 Commercial mortgage-backed securities 1,382 5 (39 ) (1) 1,348 Other asset-backed securities 1,077 7 (9 ) (1) 1,075 Redeemable preferred securities 22 5 — 27 Total debt securities 21,067 779 (206 ) 21,640 Equity securities 84 20 (2 ) 102 Total debt and equity securities (2) $ 21,151 $ 799 $ (208 ) $ 21,742 December 31, 2015 Debt securities: U.S. government securities $ 1,804 $ 69 $ (1 ) $ 1,872 States, municipalities and political subdivisions 4,890 244 (9 ) 5,125 U.S. corporate securities 7,982 340 (147 ) 8,175 Foreign securities 2,910 148 (61 ) 2,997 Residential mortgage-backed securities 914 17 (6 ) 925 Commercial mortgage-backed securities 1,262 17 (9 ) (1) 1,270 Other asset-backed securities 910 3 (19 ) (1) 894 Redeemable preferred securities 33 11 — 44 Total debt securities 20,705 849 (252 ) 21,302 Equity securities 23 4 (6 ) 21 Total debt and equity securities (2) $ 20,728 $ 853 $ (258 ) $ 21,323 (1) At both December 31, 2016 and 2015 , we held securities for which we previously recognized an immaterial amount of non-credit related impairments in accumulated other comprehensive loss. These securities each had an immaterial amount of net unrealized capital gains at December 31, 2016 and 2015 , respectively. (2) Investment risks associated with our experience-rated and discontinued products generally do not impact our operating results (refer to Note 19 for additional information on our accounting for discontinued products). At December 31, 2016 , debt and equity securities with a fair value of approximately $2.9 billion , gross unrealized capital gains of $195 million and gross unrealized capital losses of $35 million and, at December 31, 2015 , debt and equity securities with a fair value of approximately $3.0 billion , gross unrealized capital gains of $209 million and gross unrealized capital losses of $68 million were included in total debt and equity securities, but support our experience-rated and discontinued products. Changes in net unrealized capital gains (losses) on these securities are not reflected in accumulated other comprehensive income. The fair value of debt securities at December 31, 2016 is shown below by contractual maturity. Actual maturities may differ from contractual maturities because securities may be restructured, called or prepaid, or we intend to sell a security prior to maturity. (Millions) Amortized Cost Fair Value Due to mature: Less than one year $ 1,380 $ 1,394 One year through five years 6,604 6,758 After five years through ten years 5,059 5,162 Greater than ten years 4,772 5,108 Residential mortgage-backed securities 793 795 Commercial mortgage-backed securities 1,382 1,348 Other asset-backed securities 1,077 1,075 Total $ 21,067 $ 21,640 Mortgage-Backed and Other Asset-Backed Securities All of our residential mortgage-backed securities at December 31, 2016 were issued by the Government National Mortgage Association, the Federal National Mortgage Association or the Federal Home Loan Mortgage Corporation and carry agency guarantees and explicit or implicit guarantees by the U.S. Government. At December 31, 2016 , our residential mortgage-backed securities had an average credit quality rating of AAA and a weighted average duration of 4.9 years. Our commercial mortgage-backed securities have underlying loans that are dispersed throughout the United States. Significant market observable inputs used to value these securities include loss severity and probability of default. At December 31, 2016 , these securities had an average credit quality rating of AAA and a weighted average duration of 6.8 years. Our other asset-backed securities have a variety of underlying collateral (e.g., automobile loans, credit card receivables, home equity loans and commercial loans). Significant market observable inputs used to value these securities include the unemployment rate, loss severity and probability of default. At December 31, 2016 , these securities had an average credit quality rating of AA- and a weighted average duration of 1.2 years. Summarized below are the debt and equity securities we held at December 31, 2016 and 2015 that were in an unrealized capital loss position, aggregated by the length of time the investments have been in that position: Less than 12 months Greater than 12 months Total (1) (Millions, except number of securities) Number of Securities Fair Value Unrealized Losses Number of Securities Fair Value Unrealized Losses Number of Securities Fair Value Unrealized Losses December 31, 2016 Debt securities: U.S. government securities 26 $ 39 $ — 1 $ 1 $ — 27 $ 40 $ — States, municipalities and political subdivisions 865 2,228 58 37 75 3 902 2,303 61 U.S. corporate securities 1,428 2,277 44 114 101 11 1,542 2,378 55 Foreign securities 649 970 27 62 76 6 711 1,046 33 Residential mortgage-backed securities 188 455 8 104 17 1 292 472 9 Commercial mortgage-backed securities 285 1,038 39 3 3 — 288 1,041 39 Other asset-backed securities 226 403 4 208 177 5 434 580 9 Total debt securities 3,667 7,410 180 529 450 26 4,196 7,860 206 Equity securities 2 3 — 8 3 2 10 6 2 Total debt and equity securities (1) 3,669 $ 7,413 $ 180 537 $ 453 $ 28 4,206 $ 7,866 $ 208 December 31, 2015 Debt securities: U.S. government securities 48 $ 67 $ — 6 $ 13 $ — 54 $ 80 $ — States, municipalities and political subdivisions 286 714 6 42 92 3 328 806 9 U.S. corporate securities 2,751 3,169 131 215 144 16 2,966 3,313 147 Foreign securities 793 1,102 50 82 89 11 875 1,191 61 Residential mortgage-backed securities 212 329 3 177 89 3 389 418 6 Commercial mortgage-backed securities 226 562 9 30 24 — 256 586 9 Other asset-backed securities 626 653 16 69 67 4 695 720 20 Total debt securities 4,942 6,596 215 621 518 37 5,563 7,114 252 Equity securities 11 — 5 5 2 1 16 2 6 Total debt and equity securities (1) 4,953 $ 6,596 $ 220 626 $ 520 $ 38 5,579 $ 7,116 $ 258 (1) At December 31, 2016 and 2015 , debt and equity securities in an unrealized capital loss position of $35 million and $68 million , respectively, and with related fair value of $890 million and $966 million , respectively, related to experience-rated and discontinued products. We reviewed the securities in the tables above and concluded that they are performing assets generating investment income to support the needs of our business. In performing this review, we considered factors such as the quality of the investment security based on research performed by our internal credit analysts and external rating agencies and the prospects of realizing the carrying value of the security based on the investment’s current prospects for recovery. At December 31, 2016 , we did not intend to sell these securities, and we did not believe it was more likely than not that we would be required to sell these securities prior to anticipated recovery of their amortized cost basis. The maturity dates for debt securities in an unrealized capital loss position at December 31, 2016 were as follows: Supporting discontinued and experience-rated products Supporting remaining products Total (Millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Due to mature: Less than one year $ 5 $ — $ 201 $ — $ 206 $ — One year through five years 70 1 2,083 28 2,153 29 After five years through ten years 288 9 1,559 43 1,847 52 Greater than ten years 317 17 1,244 51 1,561 68 Residential mortgage-backed securities 16 1 456 8 472 9 Commercial mortgage-backed securities 174 6 867 33 1,041 39 Other asset-backed securities 20 1 560 8 580 9 Total $ 890 $ 35 $ 6,970 $ 171 $ 7,860 $ 206 Mortgage Loans Our mortgage loans are collateralized by commercial real estate. During 2016 and 2015 we had the following activity in our mortgage loan portfolio: (Millions) 2016 2015 New mortgage loans $ 190 $ 213 Mortgage loans fully-repaid 173 163 Mortgage loans foreclosed 8 9 We assess our mortgage loans on a regular basis for credit impairments, and annually assign a credit quality indicator to each loan. Our credit quality indicator is internally developed and categorizes our portfolio on a scale from 1 to 7. These indicators are based upon several factors, including current loan to value ratios, property condition, market trends, creditworthiness of the borrower and deal structure. The vast majority of our mortgage loans fall into categories 2 to 4. • Category 1 - Represents loans of superior quality • Category 2 to 4 - Represents loans where credit risk is minimal to acceptable; however, these loans may display some susceptibility to economic changes. • Categories 5 and 6 - Represents loans where credit risk is not substantial, but these loans warrant management’s close attention. • Category 7 - Represents loans where collections are potentially at risk and if necessary, an impairment is recorded. Based upon our most recent assessments at December 31, 2016 and 2015 , our mortgage loans were given the following credit quality indicators: (In Millions, except credit ratings indicator) 2016 2015 1 $ 45 $ 66 2 to 4 1,449 1,467 5 and 6 17 21 7 — — Total $ 1,511 $ 1,554 At December 31, 2016 scheduled mortgage loan principal repayments were as follows: (Millions) 2017 $ 171 2018 216 2019 123 2020 166 2021 253 Thereafter 582 Net Investment Income Sources of net investment income for 2016 , 2015 and 2014 were as follows: (Millions) 2016 2015 2014 Debt securities $ 772 $ 794 $ 801 Mortgage loans 95 91 108 Other investments 82 78 76 Gross investment income 949 963 985 Investment expenses (39 ) (46 ) (39 ) Net investment income (1) $ 910 $ 917 $ 946 (1) Net investment income includes $208 million , $248 million and $289 million for 2016 , 2015 and 2014 , respectively, related to investments supporting our experience-rated and discontinued products. Realized Capital Gains/Losses Net realized capital (losses) gains for the three years ended December 31, 2016 , 2015 and 2014 , excluding amounts related to experience-rated contract holders and discontinued products, were as follows: (Millions) 2016 2015 2014 Other-than-temporary impairment (“OTTI”) losses on debt securities recognized in earnings $ (30 ) $ (64 ) $ (5 ) Other net realized capital gains (losses) 116 (1 ) 85 Net realized capital gains (losses) $ 86 $ (65 ) $ 80 The net realized capital gains in 2016 were primarily attributable to gains from the sales of debt securities and other investments, partially offset by yield-related OTTI on debt securities. The net realized capital losses in 2015 were primarily attributable to yield-related OTTI on U.S. corporate debt securities. The net realized capital gains in 2014 were primarily attributable to gains from the sales of debt and equity securities. Yield-related impairments are recognized in other comprehensive income unless we have the intention to sell the security in an unrealized capital loss position, in which case the yield-related OTTI is recognized in earnings. In 2016 and 2015 , we recognized yield-related OTTI losses of $24 million and $63 million , respectively, related to our debt securities. Yield-related OTTI losses were not significant in 2014 . We had no other individually material realized capital losses on debt or equity securities that impacted our operating results during 2016 , 2015 or 2014 . Excluding amounts related to experience-rated and discontinued products, proceeds from the sale of available for sale debt and equity securities and the related gross realized capital gains and losses for 2016 , 2015 and 2014 were as follows (1) : (Millions) 2016 2015 2014 Proceeds on sales $ 6,725 $ 4,987 $ 4,615 Gross realized capital gains 155 83 109 Gross realized capital losses 61 76 36 (1) The proceeds on sales and gross realized capital gains and losses exclude the impact of the sales of short-term debt securities which primarily relate to our investments in mutual funds. These investments were excluded from the disclosed amounts because they represent an immaterial amount of aggregate gross realized capital gains or losses and have a high volume of sales activity. Variable Interest Entities As discussed in Note 2 , we adopted the guidance of Accounting Standards Update (ASU) No. 2015-02, Amendments to the Consolidation Analysis (Topic 810) effective January 1, 2016 . As a result of adopting the new guidance, we have investments in certain hedge fund and private equity investments and real estate partnerships that are considered Variable Interest Entities (“VIE’s”). We do not have a future obligation to fund losses or debts on behalf of these investments; however, we may voluntarily contribute funds. In evaluating whether we are the primary beneficiary of a VIE, we considered several factors, including whether we (a) have the power to direct the activities that most significantly impact the VIE’s economic performance and (b) the obligation to absorb losses and the right to receive benefits that could potentially be significant to the VIE. Variable Interest Entities - Primary Beneficiary Upon adoption of the new guidance, we identified one hedge fund investment previously consolidated as a Voting Interest Entity in our balance sheets and operating results that is determined to be a VIE under the new guidance. The investment represents a majority-owned hedge fund where we are the investment manager and have the power to direct the activities that most significantly impact the VIE’s economic performance, including determining the hedge fund’s investment strategy. Accordingly, we are the primary beneficiary and will continue to consolidate the investment in our operating results. The fund invests in additional hedge funds that are VIEs; however, we are not the primary beneficiary of these underlying funds as discussed in further detail below. Substantially all of the assets of the VIE hedge fund are comprised of hedge fund investments reported as long-term investments on our balance sheets. The VIE hedge fund had no material liabilities at December 31, 2016 or 2015. The total amount of the VIE hedge fund’s assets included in long term investments on our balance sheets at December 31, 2016 and 2015 was $472 million and $477 million , respectively. Variable Interest Entities - Other Variable Interest Holder Our involvement with VIEs where we are not determined to be the primary beneficiary consists of the following: • Hedge fund and private equity investments - We invest in hedge fund and private equity investments in order to generate investment returns for our investment portfolio supporting our businesses. • Real estate partnerships - We invest in various real estate partnerships including those that construct, own and manage low-income housing developments. For the low income housing development investments, substantially all of the projected benefits to us are from tax credits and other tax benefits. We are not the primary beneficiary of these investments because the nature of our involvement with the activities of these VIEs does not give us the power to direct the activities that most significantly impact their economic performance. We record the amount of our investment in these VIEs as long-term investments on our balance sheets and recognize our share of each VIE’s income or losses in earnings. Our maximum exposure to loss from these VIEs is limited to our investment balances as disclosed below and the risk of recapture of tax credits related to the real estate partnerships previously recognized, which we do not consider significant. The total amount of other variable interest holder VIE assets included in long term investments on our balance sheets at December 31, 2016 and 2015 were as follows: (Millions) December 31, December 31, 2015 Hedge fund investments $ 384 $ 418 Private equity investments 454 443 Real estate partnerships 278 254 Total $ 1,116 $ 1,115 The carrying value of the total assets and liabilities of our other variable interest holder VIE investments at December 31, 2016 and 2015 were as follows: (Millions) December 31, December 31, 2015 Assets: Hedge fund investments $ 32,926 $ 33,066 Private equity investments 25,368 28,552 Real estate partnerships 6,743 6,809 Total $ 65,037 $ 68,427 Liabilities: Hedge fund investments $ 2,819 $ 3,535 Private equity investments 2,354 3,236 Real estate partnerships 4,938 5,045 Total $ 10,111 $ 11,816 Non-controlling (Minority) Interests At December 31, 2016 and 2015 , continuing business non-controlling interests were $62 million and $65 million , respectively, primarily related to third party interests in our investment holdings as well as third party interests in certain of our operating entities. The non-controlling entities’ share was included in total equity. Net loss attributable to non-controlling interests was $15 million during 2016. Net income attributable to non-controlling interests was $5 million and $4 million during 2015 and 2014, respectively. These non-controlling interests did not have a material impact on our financial position or operating results.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2016
Financial Instruments [Abstract]
Financial Instruments	5. Fair Value The preparation of our consolidated financial statements in accordance with GAAP requires certain of our assets and liabilities to be reflected at their fair value, and others on another basis, such as an adjusted historical cost basis. In this note, we provide details on the fair value of financial assets and liabilities and how we determine those fair values. We present this information for those financial instruments that are measured at fair value for which the change in fair value impacts net income attributable to Aetna or other comprehensive income separately from other financial assets and liabilities. Financial Instruments Measured at Fair Value in our Balance Sheets Certain of our financial instruments are measured at fair value in our balance sheets. The fair values of these instruments are based on valuations that include inputs that can be classified within one of three levels of a hierarchy established by GAAP. The following are the levels of the hierarchy and a brief description of the type of valuation information (“inputs”) that qualifies a financial asset or liability for each level: ◦ Level 1 – Unadjusted quoted prices for identical assets or liabilities in active markets. ◦ Level 2 – Inputs other than Level 1 that are based on observable market data. These include: quoted prices for similar assets in active markets, quoted prices for identical assets in inactive markets, inputs that are observable that are not prices (such as interest rates and credit risks) and inputs that are derived from or corroborated by observable markets. ◦ Level 3 – Developed from unobservable data, reflecting our own assumptions. Financial assets and liabilities are classified based upon the lowest level of input that is significant to the valuation. When quoted prices in active markets for identical assets and liabilities are available, we use these quoted market prices to determine the fair value of financial assets and liabilities and classify these assets and liabilities in Level 1. In other cases where a quoted market price for identical assets and liabilities in an active market is either not available or not observable, we estimate fair value using valuation methodologies based on available and observable market information or by using a matrix pricing model. These financial assets and liabilities would then be classified in Level 2. If quoted market prices are not available, we determine fair value using broker quotes or an internal analysis of each investment’s financial performance and cash flow projections. Thus, financial assets and liabilities may be classified in Level 3 even though there may be some significant inputs that may be observable. The following is a description of the valuation methodologies used for our financial assets and liabilities that are measured at fair value, including the general classification of such assets and liabilities pursuant to the valuation hierarchy. Debt Securities – Where quoted prices are available in an active market, our debt securities are classified in Level 1 of the fair value hierarchy. Our Level 1 debt securities are comprised primarily of U.S. Treasury securities. The fair values of our Level 2 debt securities are obtained using models such as matrix pricing, which use quoted market prices of debt securities with similar characteristics, or discounted cash flows to estimate fair value. We review these prices to ensure they are based on observable market inputs that include, but are not limited to, quoted prices for similar assets in active markets, quoted prices for identical assets in inactive markets and inputs that are observable but not prices (for example, interest rates and credit risks). We also review the methodologies and the assumptions used to calculate prices from these observable inputs. On a quarterly basis, we select a sample of our Level 2 debt securities’ prices and compare them to prices provided by a secondary source. Variances over a specified threshold are identified and reviewed to confirm the price provided by the primary source represents an appropriate estimate of fair value. In addition, our internal investment team consistently compares the prices obtained for select Level 2 debt securities to the team’s own independent estimates of fair value for those securities. We obtained one price for each of our Level 2 debt securities and did not adjust any of these prices at December 31, 2016 or 2015 . We also value certain debt securities using Level 3 inputs. For Level 3 debt securities, fair values are determined by outside brokers or, in the case of certain private placement securities, are priced internally. Outside brokers determine the value of these debt securities through a combination of their knowledge of the current pricing environment and market flows. We obtained one non-binding broker quote for each of these Level 3 debt securities and did not adjust any of these quotes at December 31, 2016 or 2015 . The total fair value of our broker quoted debt securities was $80 million and $78 million at December 31, 2016 and 2015 , respectively. Examples of these broker quoted Level 3 debt securities include certain U.S. and foreign corporate securities and certain of our commercial mortgage-backed securities as well as other asset-backed securities. For some of our private placement securities, our internal staff determines the value of these debt securities by analyzing spreads of corporate and sector indices as well as interest spreads of comparable public bonds. Examples of these private placement Level 3 debt securities include certain U.S. and foreign securities and certain tax-exempt municipal securities. Equity Securities – We currently have two classifications of equity securities: those that are publicly traded and those that are privately placed. Our publicly-traded securities are classified in Level 1 because quoted prices are available for these securities in an active market. For privately placed equity securities, there is no active market; therefore, we classify these securities in Level 3 because we price these securities through an internal analysis of each investment’s financial statements and cash flow projections. Significant unobservable inputs consist of earnings and revenue multiples, discount for lack of marketability and comparability adjustments. An increase or decrease in any of these unobservable inputs would result in a change in the fair value measurement, which may be significant. Derivatives – Where quoted prices are available in an active market, our derivatives are classified in Level 1. Certain of our derivative instruments are valued using models that primarily use market observable inputs and therefore are classified in Level 2 because they are traded in markets where quoted market prices are not readily available. Financial assets and liabilities measured at fair value on a recurring basis in our balance sheets at December 31, 2016 and 2015 were as follows: (Millions) Level 1 Level 2 Level 3 Total December 31, 2016 Assets: Debt securities: U.S. government securities $ 1,514 $ 180 $ — $ 1,694 States, municipalities and political subdivisions — 5,137 1 5,138 U.S. corporate securities — 8,395 80 8,475 Foreign securities — 3,067 21 3,088 Residential mortgage-backed securities — 795 — 795 Commercial mortgage-backed securities — 1,348 — 1,348 Other asset-backed securities — 1,075 — 1,075 Redeemable preferred securities — 26 1 27 Total debt securities 1,514 20,023 103 21,640 Equity securities 59 — 43 102 Derivatives — — — — Total $ 1,573 $ 20,023 $ 146 $ 21,742 Liabilities: Derivatives $ — $ — $ — $ — December 31, 2015 Assets: Debt securities: U.S. government securities $ 1,671 $ 201 $ — $ 1,872 States, municipalities and political subdivisions — 5,124 1 5,125 U.S. corporate securities — 8,111 64 8,175 Foreign securities — 2,972 25 2,997 Residential mortgage-backed securities — 925 — 925 Commercial mortgage-backed securities — 1,270 — 1,270 Other asset-backed securities — 894 — 894 Redeemable preferred securities — 39 5 44 Total debt securities 1,671 19,536 95 21,302 Equity securities 2 — 19 21 Derivatives — 20 — 20 Total $ 1,673 $ 19,556 $ 114 $ 21,343 Liabilities: Derivatives $ — $ 88 $ — $ 88 There were no transfers between Levels 1 and 2 during the years ended December 31, 2016 and 2015 . The changes in the balances of Level 3 financial assets during 2016 were as follows: (Millions) Foreign securities U.S. corporate securities Equity securities Other Total Beginning balance $ 25 $ 64 $ 19 $ 6 $ 114 Net realized and unrealized capital (losses) gains: Included in earnings — (15 ) — — (15 ) Included in other comprehensive income — (4 ) 11 (3 ) 4 Other (1) — — 3 — 3 Purchases 16 41 10 33 100 Sales (8 ) (3 ) — (5 ) (16 ) Settlements (2 ) (3 ) — — (5 ) Transfers out of Level 3, net (10 ) — — (29 ) (39 ) Ending balance $ 21 $ 80 $ 43 $ 2 $ 146 (1) Reflects realized and unrealized capital gains and losses on investments supporting our experience-rated and discontinued products, which do not impact our operating results. The changes in the balances of Level 3 financial assets during 2015 were as follows: (Millions) Foreign securities U.S. corporate securities Equity securities Other Total Beginning balance $ 32 $ 58 $ 18 $ 54 $ 162 Net realized and unrealized capital gains (losses): Included in earnings — (6 ) — — (6 ) Included in other comprehensive income — 2 2 — 4 Other (1) (1 ) — (3 ) — (4 ) Purchases — 11 2 24 37 Sales (5 ) (1 ) — — (6 ) Settlements (1 ) — — (9 ) (10 ) Transfers out of Level 3, net — — — (63 ) (63 ) Ending balance $ 25 $ 64 $ 19 $ 6 $ 114 (1) Reflects realized and unrealized capital gains and losses on investments supporting our experience-rated and discontinued products, which do not impact our operating results. The total gross transfers into (out of) Level 3 during the years ended December 31, 2016 and 2015 were as follows: (Millions) 2016 2015 Gross transfers into Level 3 $ — $ 1 Gross transfers out of Level 3 (39 ) (64 ) Net transfers out of Level 3 $ (39 ) $ (63 ) Gross transfers out of Level 3 during 2016 primarily related to commercial mortgage-backed securities. Gross transfers out of Level 3 during 2015 primarily related to other asset-backed securities. Financial Instruments Not Measured at Fair Value in our Balance Sheets The following is a description of the valuation methodologies used for estimating the fair value of our financial assets and liabilities that are carried on our balance sheets at adjusted cost or contract value. Mortgage loans: Fair values are estimated by discounting expected mortgage loan cash flows at market rates that reflect the rates at which similar loans would be made to similar borrowers. These rates reflect our assessment of the creditworthiness of the borrower and the remaining duration of the loans. The fair value estimates of mortgage loans of lower credit quality, including problem and restructured loans, are based on the estimated fair value of the underlying collateral. Bank loans: Where fair value is determined by quoted market prices of bank loans with similar characteristics, our bank loans are classified in Level 2. For bank loans classified in Level 3, fair value is determined by outside brokers using their internal analyses through a combination of their knowledge of the current pricing environment and market flows. Equity securities: Certain of our equity securities are carried at cost. The fair values of our cost-method investments are not estimated if there are no identified events or changes in circumstances that may have a significant adverse effect on the fair value of the investment. Investment contract liabilities: • With a fixed maturity : Fair value is estimated by discounting cash flows at interest rates currently being offered by, or available to, us for similar contracts. • Without a fixed maturity : Fair value is estimated as the amount payable to the contract holder upon demand. However, we have the right under such contracts to delay payment of withdrawals that may ultimately result in paying an amount different than that determined to be payable on demand. Long-term debt: Fair values are based on quoted market prices for the same or similar issued debt or, if no quoted market prices are available, on the current rates estimated to be available to us for debt of similar terms and remaining maturities. The carrying value and estimated fair value classified by level of fair value hierarchy for our financial instruments carried on our balance sheets at adjusted cost or contract value at December 31, 2016 and 2015 were as follows: Carrying Value Estimated Fair Value (Millions) Level 1 Level 2 Level 3 Total December 31, 2016 Assets: Mortgage loans $ 1,511 $ — $ — $ 1,540 $ 1,540 Bank loans 8 — — 8 8 Equity securities (1) 35 N/A N/A N/A N/A Liabilities: Investment contract liabilities: With a fixed maturity 8 — — 8 8 Without a fixed maturity 378 — — 364 364 Long-term debt 20,661 — 21,468 — 21,468 Carrying Value Estimated Fair Value (Millions) Level 1 Level 2 Level 3 Total December 31, 2015 Assets: Mortgage loans $ 1,554 $ — $ — $ 1,599 $ 1,599 Bank loans 193 — 180 8 188 Equity securities (1) 35 N/A N/A N/A N/A Liabilities: Investment contract liabilities: With a fixed maturity 9 — — 9 9 Without a fixed maturity 371 — — 351 351 Long-term debt 7,785 — 8,227 — 8,227 (1) It was not practical to estimate the fair value of these cost-method investments as it represents shares of unlisted companies. Separate Accounts Measured at Fair Value in our Balance Sheets Separate Accounts assets in our Large Case Pensions segment represent funds maintained to meet specific objectives of contract holders. Since contract holders bear the investment risk of these assets, a corresponding Separate Accounts liability has been established equal to the assets. These assets and liabilities are carried at fair value. Net investment income and capital gains and losses accrue directly to such contract holders. The assets of each account are legally segregated and are not subject to claims arising from our other businesses. Deposits, withdrawals, net investment income and realized and unrealized capital gains and losses on Separate Accounts assets are not reflected in our statements of income, shareholders’ equity or cash flows. Separate Accounts assets include debt and equity securities and derivative instruments. The valuation methodologies used for these assets are similar to the methodologies described above in this Note 5 . Separate Accounts assets also include investments in common/collective trusts that are carried at fair value. Common/collective trusts invest in other investment funds otherwise known as the underlying funds. The Separate Accounts’ interests in the common/collective trust funds are based on the fair values of the investments of the underlying funds and therefore are classified in Level 2. The assets in the underlying funds primarily consist of equity securities. Investments in common/collective trust funds are valued at their respective net asset value per share/unit on the valuation date. Separate Accounts financial assets at December 31, 2016 and 2015 were as follows: 2016 2015 (Millions) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Debt securities $ 766 $ 2,378 $ — $ 3,144 $ 751 $ 2,382 $ 4 $ 3,137 Equity securities 166 6 — 172 170 5 — 175 Common/collective trusts — 582 — 582 — 540 — 540 Total (1) $ 932 $ 2,966 $ — $ 3,898 $ 921 $ 2,927 $ 4 $ 3,852 (1) Excludes $93 million and $183 million of cash and cash equivalents and other receivables at December 31, 2016 and 2015 , respectively. During 2016 and 2015 , we had an immaterial amount of Level 3 Separate Accounts financial assets and an immaterial amount of gross transfers of Separate Accounts financial assets into or out of Level 3. During 2016 and 2015, there were no transfers of Separate Accounts financial assets between Levels 1 and 2. Offsetting Financial Assets and Liabilities Certain financial assets and liabilities are offset in our balance sheets or are subject to master netting arrangements or similar agreements with the applicable counterparty. Financial assets, including derivative assets, subject to offsetting and enforceable master netting arrangements as of December 31, 2016 and December 31, 2015 were as follows: Gross Amounts of Recognized Assets (1) Gross Amounts Not Offset In the Balance Sheets Financial Instruments Cash Collateral Received (Millions) Net Amount December 31, 2016 Derivatives $ — $ 17 $ — $ 17 Total $ — $ 17 $ — $ 17 December 31, 2015 Derivatives $ 20 $ 12 $ (17 ) $ 15 Total $ 20 $ 12 $ (17 ) $ 15 (1) There were no amounts offset in our balance sheets at December 31, 2016 or December 31, 2015 . Financial liabilities, including derivative liabilities, subject to offsetting and enforceable master netting arrangements as of December 31, 2016 and December 31, 2015 were as follows: Gross Amounts of Recognized Liabilities (1) Gross Amounts Not Offset In the Balance Sheets Financial Instruments Cash Collateral Paid (Millions) Net Amount December 31, 2016 Derivatives $ — $ — $ — $ — Total $ — $ — $ — $ — December 31, 2015 Derivatives $ 88 $ — $ (90 ) $ (2 ) Total $ 88 $ — $ (90 ) $ (2 ) (1) There were no amounts offset in our balance sheets at December 31, 2016 or December 31, 2015 .

Goodwill and Other Acquired Int

Goodwill and Other Acquired Intangible Assets	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Acquired Intangible Assets	6. Goodwill and Other Acquired Intangible Assets The change in the carrying amount of goodwill for our reportable segments for the years ended December 31, 2016 and 2015 was as follows: (Millions) Health Care Group Insurance Total Company Balance at January 1, 2015 $ 10,500 $ 113 $ 10,613 Acquisitions 12 — 12 Dispositions — — — Subsequent adjustments 12 — 12 Balance at December 31, 2015 10,524 113 10,637 Acquisitions — — — Dispositions — — — Subsequent adjustments — — — Balance at December 31, 2016 $ 10,524 $ 113 $ 10,637 No goodwill is allocated to the Large Case Pensions segment. The increase in goodwill during 2015 was due to purchase accounting adjustments related to the bswift acquisition and goodwill associated with an immaterial acquisition. Other acquired intangible assets at December 31, 2016 and 2015 were comprised of the following: (Millions) Cost Accumulated Amortization Net Balance Amortization Period (Years) 2016 Provider networks $ 1,254 $ 694 $ 560 12-25 (1) Customer lists 1,166 485 681 3-14 (1) Value of business acquired 149 92 57 20 Technology 176 123 53 4-10 Other 10 4 6 10-15 Definite-lived trademarks 170 107 63 5-20 Indefinite-lived trademarks 22 — 22 Total other acquired intangible assets $ 2,947 $ 1,505 $ 1,442 2015 Provider networks $ 1,254 $ 632 $ 622 12-25 (1) Customer lists 1,165 374 791 5-14 (1) Value of business acquired 149 80 69 20 Technology 176 93 83 4-10 Other 10 3 7 2-15 Definite-lived trademarks 170 76 94 5-20 Indefinite-lived trademarks 22 — 22 Total other acquired intangible assets $ 2,946 $ 1,258 $ 1,688 (1) The amortization period for our provider networks and customer lists includes an assumption of renewal or extension of these arrangements. At both December 31, 2016 and 2015 , the periods prior to the next renewal or extension for our provider networks primarily ranged from 1 to 3 years, and the period prior to the next renewal or extension for our customer lists was 1 year. Any costs related to the renewal or extension of these contracts are expensed as incurred. We estimate annual pre-tax amortization for other acquired intangible assets over the next five years to be as follows: (Millions) 2017 $ 234 2018 198 2019 192 2020 180 2021 156

Health Care and Other Insurance

Health Care and Other Insurance Liabilities	12 Months Ended
	Dec. 31, 2016
Health Care and Other Insurance Liabilities [Abstract]
Short-Duration Insurance and Deposit Contracts [Text Block]	7. Health Care and Other Insurance Liabilities Health Care Costs Payable The following is information about incurred and cumulative paid Health Care claims development as of December 31, 2016, net of reinsurance, and the total IBNR liabilities plus expected development on reported claims included within the net incurred claims amounts. Refer to Note 2 for information on how we estimate our IBNR reserve and health care costs payable as well as changes to those methodologies, if any. Our estimate of IBNR liabilities is primarily based on trend and completion factors. Claim frequency is not used in the calculation of our liability. In addition, it is impracticable to disclose claim frequency information for health care claims due to our inability to gather consistent claim frequency information across our multiple claims processing systems. Any claim frequency count disclosure would not be comparable across our different claim processing systems and would not be consistent from period to period based on the volume of claims processed through each system. As a result, we have not included health care claim count frequency in the disclosures included below. The information about incurred and paid Health Care claims development for the year ended December 31, 2015 is presented as required unaudited supplemental information. Incurred Health Care Claims, Net of Reinsurance (Millions) For the Years Ended December 31, Date of Service 2015 2016 (Unaudited) 2015 $ 41,825 $ 41,114 2016 44,110 Total $ 85,224 Cumulative Paid Health Care Claims, Net of Reinsurance (Millions) For the Years Ended December 31, Date of Service 2015 2016 (Unaudited) 2015 $ 35,735 $ 40,947 2016 37,888 Total $ 78,835 All outstanding liabilities for health care costs payable prior to 2015, net of reinsurance 66 Total outstanding liabilities for health care costs payable, net of reinsurance $ 6,455 At December 31, 2016, total Health Care IBNR liabilities plus expected development on reported claims totaled approximately $5.6 billion . Substantially all of the total Health Care IBNR liabilities plus expected development on reported claims at December 31, 2016 related to the current year. The reconciliation of the December 31, 2016 Health Care net incurred and paid claims development tables to the health care costs payable liability in the consolidated balance sheet is as follows: (Millions) December 31, 2016 Short-duration health care costs payable, net of reinsurance $ 6,455 Reinsurance recoverables 5 Insurance lines other than short duration 98 Total health care costs payable $ 6,558 The following table shows the components of the change in health care costs payable during 2016 , 2015 and 2014 : (Millions) 2016 2015 2014 Health care costs payable, beginning of the period $ 6,306 $ 5,621 $ 4,547 Less: Reinsurance recoverables 4 6 8 Health care costs payable, beginning of the period, net 6,302 5,615 4,539 Acquisition of businesses — — 29 Add: Components of incurred health care costs Current year 45,019 42,553 41,328 Prior years (764 ) (841 ) (581 ) Total incurred health care costs 44,255 41,712 40,747 Less: Claims paid Current year 38,700 36,389 35,851 Prior years 5,304 4,636 3,849 Total claims paid 44,004 41,025 39,700 Health care costs payable, end of period, net 6,553 6,302 5,615 Add: Reinsurance recoverables 5 4 6 Health care costs payable, end of period $ 6,558 $ 6,306 $ 5,621 Our estimates of prior years’ health care costs payable decreased in each of 2016 , 2015 and 2014 , respectively, because claims settled for amounts less than originally estimated, primarily due to lower health care cost trends as well as the actual claim submission time being faster than we assumed in establishing our health care costs payable in the prior year. This development does not directly correspond to an increase in our current year operating results as these reductions were offset by estimated current period health care costs when we established our estimate of the current year health care costs payable. Long-Term Disability Unpaid Claims The following is information about incurred and cumulative paid long-term disability claims development as of December 31, 2016, net of reinsurance, and the total IBNR liabilities plus expected development on reported claims included within the net incurred claims amounts. Refer to Note 2 for information on how we estimate our IBNR reserve and unpaid long-term disability claims liability as well as changes to those methodologies. We define a unique claim in our long-term disability Insured products based on the date an individual is placed on disability. There have been no significant changes to the methodologies or assumptions used to determine claim frequency in 2016. The information about incurred and paid long-term disability claims development for the years ended December 31, 2011 through 2015 is presented as required unaudited supplemental information. At December 31, 2016, we have disclosed six years of claims development and will add one year going forward in each subsequent year until we reach ten years of disclosure. Incurred Long-Term Disability Claims, Net of Reinsurance For the Years Ended December 31, As of December 31, 2016 (Millions) (Unaudited) Total IBNR liabilities plus expected development on reported claims Cumulative number of reported claims (Actual) Date of Service 2011 2012 2013 2014 2015 2016 2011 $ 360 $ 346 $ 335 $ 338 $ 342 $ 340 $ 2 6,988 2012 413 394 385 381 384 1 8,171 2013 473 482 463 478 2 10,104 2014 512 490 481 8 11,622 2015 533 504 18 12,924 2016 573 270 11,464 Total $ 2,760 Cumulative Paid Long-Term Disability Claims, Net of Reinsurance (Millions) For the Years Ended December 31, (Unaudited) Date of Service 2011 2012 2013 2014 2015 2016 2011 $ 20 $ 96 $ 144 $ 173 $ 199 $ 219 2012 24 119 177 208 236 2013 32 151 224 264 2014 35 161 242 2015 40 181 2016 48 Total 1,190 All outstanding unpaid long-term disability claims prior to 2011, net of reinsurance 754 Total outstanding unpaid long-term disability claims, net of reinsurance $ 2,324 The reconciliation of the December 31, 2016 short-duration long-term disability net incurred and paid claims development tables to the short-duration long-term disability unpaid claims liability is as follows: December 31, 2016 Short-duration long-term disability unpaid claims, net of reinsurance $ 2,324 Reinsurance recoverables 26 Impact of discounting (446 ) Total short-duration long-term disability unpaid claims $ 1,904 The following is information on long-term disability unpaid claims liabilities presented at present value: Unpaid Long-Term Disability Claims Liabilities Presented at Present Value Carrying amount of unpaid claims liabilities Discount rate Aggregate amount of discount As of December 31, As of December 31, As of December 31, (Millions) 2016 2015 2016 2015 2016 2015 Long-term disability $ 1,878 $ 1,793 5.0 % 5.4 % $ 446 $ 473 Interest accretion in the amounts of $97 million , $97 million and $93 million were recognized for the years ended December 31, 2016 , 2015 and 2014 , respectively, within current and future benefits in our statements of income. The following is required unaudited supplementary information about average historical long-term disability claims duration as of December 31, 2016: Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance (Unaudited) Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Long-term disability 7.3 % 25.3 % 15.0 % 8.2 % 6.9 % 5.8 % The following table shows the components of the change in unpaid long-term disability claims during 2016, 2015 and 2014: (Millions) 2016 2015 2014 Long-term disability unpaid claims beginning of the period $ 1,819 $ 1,772 $ 1,685 Less: Reinsurance recoverables 27 27 28 Long-term disability unpaid claims, beginning of the period, net 1,792 1,745 1,657 Add: Components of incurred claims Current year 529 488 465 Prior years 41 (4 ) 22 Total incurred claims 570 484 487 Less: Claims paid Current year 48 40 35 Prior years 436 397 364 Total claims paid 484 437 399 Long-term disability unpaid claims, end of period, net 1,878 1,792 1,745 Add: Reinsurance recoverables 26 27 27 Long-term disability unpaid claims, end of period $ 1,904 $ 1,819 $ 1,772 Our estimates of prior years’ long-term disability unpaid claims liability were relatively consistent with actual results in each of 2016, 2015 and 2014, respectively. The reconciliation of the short-duration long-term disability unpaid claims liability to the total unpaid claims liability in the consolidated balance sheet is as follows for 2016 , 2015 and 2014 : (Millions) 2016 2015 2014 Short duration long-term disability unpaid claims $ 1,904 $ 1,819 $ 1,772 Term life unpaid claims 481 493 518 Other unpaid claims 119 116 106 Total unpaid claims $ 2,504 $ 2,428 $ 2,396

The ACA's Reinsurance, Risk Adj

The ACA's Reinsurance, Risk Adjustment and Risk Corridor	12 Months Ended
	Dec. 31, 2016
Health Care Reform [Abstract]
Health Care Reform [Text Block]	8. The ACA’s Reinsurance, Risk Adjustment and Risk Corridor We participate in certain Public Exchanges established pursuant to the ACA. Under regulations established by HHS, HHS pays us a portion of the Premium Subsidy and the Cost Sharing Subsidy for low-income individual Public Exchange members. In addition, HHS administers the 3Rs risk management programs. Our current net receivable (payable) related to the 3Rs risk management programs at December 31, 2016 and 2015 was as follows: At December 31, 2016 At December 31, 2015 (Millions) Reinsurance Risk Adjustment Risk Corridor Reinsurance Risk Adjustment Risk Corridor Total current net receivable (payable) $ 202 $ (690 ) $ (10 ) $ 395 $ (710 ) $ (8 ) At December 31, 2016, we estimate that we are entitled to receive a total of $465 million from HHS under the three-year ACA risk corridor program for the 2014 through 2016 program years. In November 2016, HHS announced that all 2015 ACA risk corridor collections will be used to pay a portion of the balances on the 2014 ACA risk corridor payments. At December 31, 2016, we did not record any ACA risk corridor receivables related to the 2016 or 2015 program years or any amount in excess of HHS’s announced pro-rated funding amount for the 2014 program year because payments from HHS are uncertain. We expect to perform an annual final reconciliation and settlement with HHS of the Cost Sharing Subsidy and 3Rs in each subsequent year, except for the final reconciliation and settlement of the 2014 Cost Sharing Subsidy which occurred in 2016. Refer to Note 2 for additional information.

Debt

Debt	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Debt	9. Debt Long-term debt The carrying value of our long-term debt at December 31, 2016 and 2015 was as follows: (Millions) 2016 2015 Senior notes, 5.95% due March 2017 (1) $ 386 $ 402 Senior notes, 1.75% due May 2017 (1) 250 249 Senior notes, 1.5% due November 2017 (1) 499 498 Senior notes, floating rate due December 2017 (1) 499 — Senior notes, 1.7% due June 2018 997 — Senior notes, 2.2% due March 2019 374 373 Senior notes, 1.9% due June 2019 1,642 — Senior notes, 3.95% due September 2020 745 743 Senior notes, 2.4% due June 2021 1,839 — Senior notes, 5.45% due June 2021 661 675 Senior notes, 4.125% due June 2021 495 494 Senior notes, 2.75% due November 2022 986 983 Senior notes, 2.8% due June 2023 1,290 — Senior notes, 3.5% due November 2024 742 741 Senior notes, 3.2% due June 2026 2,771 — Senior notes, 4.25% due June 2036 1,480 — Senior notes, 6.625% due June 2036 765 765 Senior notes, 6.75% due December 2037 527 527 Senior notes, 4.5% due May 2042 478 477 Senior notes, 4.125% due November 2042 489 489 Senior notes, 4.75% due March 2044 371 371 Senior notes, 4.375% due June 2046 2,375 — Total long-term debt 20,661 7,787 Less current portion of long-term debt 1,634 — Less credit facility issuance costs — 2 Total long-term debt, less current portion and credit facility issuance costs $ 19,027 $ 7,785 (1) At December 31, 2016 , our 5.95% senior notes due March 2017, 1.75% senior notes due May 2017, 1.5% senior notes due November 2017 and floating rate senior notes due December 2017 are each classified as current in our consolidated balance sheet. At December 31, 2016 the amount of future maturities of our long-term debt are as follows: (Millions) 2017 $ 1,634 2018 997 2019 2,016 2020 745 2021 2,995 Thereafter 12,274 2016 Senior Notes; Long-Term Debt and Bridge Credit Agreement In June 2016, in connection with the Humana Acquisition, we issued the 2016 senior notes, which are comprised of: $500 million of floating rate senior notes due December 2017, $1.0 billion of 1.7% senior notes due June 2018, approximately $1.7 billion of 1.9% senior notes due June 2019, approximately $1.9 billion of 2.4% senior notes due June 2021, $1.3 billion of 2.8% senior notes due June 2023, $2.8 billion of 3.2% senior notes due June 2026, $1.5 billion of 4.25% senior notes due June 2036 and $2.4 billion of 4.375% senior notes due June 2046. As a result of the termination of the Merger Agreement, we will redeem all of the $10.2 billion aggregate principal amount of the 2016 senior notes that are due in 2019, 2021, 2026, 2036 and 2046 at a redemption price equal to 101% of the aggregate principal amount of those notes plus accrued and unpaid interest. We will redeem those notes on or about March 16, 2017, and we expect to fund the redemption with the proceeds of the 2016 senior notes. On July 30, 2015, we entered into a $13.0 billion 364-day senior unsecured bridge credit agreement (the “Bridge Credit Agreement”) with a group of fifteen lenders. In connection with the closing of the 2016 senior notes, we terminated the Bridge Credit Agreement effective June 9, 2016. There were no amounts outstanding under the Bridge Credit Agreement at any time during the year ended December 31, 2016 . Early Extinguishment of Long-Term Debt November 2014 On November 3, 2014, we announced the redemption for cash of the entire $496 million aggregate principal amount outstanding of our 6.50% senior notes due 2018. The redemption of these notes occurred on December 3, 2014 (the “December Redemption Date”) at a redemption price that included a make-whole premium, plus interest accrued and unpaid at the December Redemption Date. We financed the redemption by issuing $750 million of 3.5% senior notes due 2024 (the “November 2014 Senior Notes”). As a result of the redemption, in the fourth quarter of 2014, we recorded a loss on the early extinguishment of long-term debt of $58 million ( $89 million pretax). In April 2014, we entered into an interest rate swap with a notional value of $250 million . We designated this swap as a cash flow hedge against interest rate exposure related to the forecasted future issuance of fixed-rate debt to be primarily used to refinance long-term debt maturing in 2018. In November 2014, prior to issuing the November 2014 Senior Notes used to refinance our 6.50% senior notes due 2018 and for general corporate purposes, we terminated this swap and paid an aggregate of $15 million to the swap counterparty upon termination. We performed a final effectiveness test upon termination of this swap and determined there was $3 million pretax of ineffectiveness that arose due to the actual debt issuance date being earlier than forecasted. The ineffectiveness was recorded as a realized capital loss in the fourth quarter of 2014. The effective portion of the hedge loss of $12 million pretax was recorded in accumulated other comprehensive loss, net of tax, and is being amortized as an increase to interest expense over the first 20 semi-annual interest payments of the November 2014 Senior Notes. March 2014 On February 7, 2014, we announced the redemption for cash of the entire $750 million aggregate principal amount outstanding of our 6.0% senior notes due 2016. The redemption of these notes occurred on March 14, 2014 (the “March Redemption Date”) at a redemption price that included a make-whole premium, plus interest accrued and unpaid at the March Redemption Date. We financed the redemption by issuing $375 million of 2.2% senior notes due 2019 and $375 million of 4.75% senior notes due 2044 (collectively, the “March 2014 Senior Notes”), together with other available resources. As a result of the redemption, in the first quarter of 2014, we recorded a loss on the early extinguishment of long-term debt of $60 million ( $92 million pretax). During June and July 2012, we entered into two interest rate swaps with an aggregate notional value of $375 million . We designated these swaps as cash flow hedges against interest rate exposure related to the forecasted future issuance of fixed-rate debt to refinance our 6.0% senior notes due 2016. In March 2014, prior to issuing the March 2014 Senior Notes used to refinance our 6.0% senior notes due 2016, we terminated these swaps and received an aggregate of $34 million from the swap counterparties upon termination. We performed a final effectiveness test upon termination of these swaps and determined there was $12 million pretax of ineffectiveness that arose due to the actual debt issuance date being earlier than forecasted. The ineffectiveness was recorded as a realized capital gain in the first quarter of 2014. The effective portion of the hedge gain of $22 million pretax was recorded in accumulated other comprehensive loss, net of tax, and is being amortized as a reduction to interest expense over the first 20 semi-annual interest payments associated with the $375 million of 4.75% senior notes due 2044. Cash Flow Hedges In 2015 and 2016, we entered into various interest rate swaps and treasury rate locks with an aggregate notional value of $3.5 billion . We designated these interest rate swaps and treasury rate locks as cash flow hedges against interest rate exposure related to the forecasted future issuance of fixed-rate debt to be primarily used to finance a portion of the purchase price of the Humana Acquisition. During the second quarter of 2016, prior to issuing the 2016 senior notes, we terminated interest rate swaps with an aggregate notional value of $2.3 billion and paid an aggregate of $193 million to the swap counterparties upon termination. We performed a final effectiveness test upon the termination of each swap, and the effective portion of the hedge loss of $193 million was recorded in accumulated other comprehensive loss, net of tax, as the forecasted future issuance of fixed-rate debt associated with the Humana Acquisition remained probable of occurring at the time of termination. Upon termination of the interest rate swaps in the second quarter of 2016, we concurrently entered into treasury rate locks with an aggregate notional value of $2.3 billion to replace the vacated hedged positions. The treasury rate locks were designated as cash flow hedges against interest rate exposure related to the forecasted future issuance of fixed-rate debt to be primarily used to finance a portion of the purchase price of the Humana Acquisition. In June 2016, in conjunction with the issuance of the 2016 senior notes, we terminated outstanding interest rate swaps and treasury rate locks with an aggregate notional value of $3.5 billion and paid an aggregate of $51 million to the hedge counterparties upon termination. We performed a final effectiveness test upon termination of each interest rate swap and treasury rate lock, and the effective portion of the hedge loss of $51 million was recorded in accumulated other comprehensive loss, net of tax. Upon the redemption of certain of the 2016 senior notes as described above, the remaining unamortized effective portion of the hedge loss recorded in accumulated other comprehensive income will be recognized in net income upon such redemption for each of the cash flow hedges discussed above. In March 2014, we entered into two interest rate swaps with an aggregate notional value of $500 million . We designated these swaps as cash flow hedges against interest rate exposure related to the forecasted future issuance of fixed-rate debt to be primarily used to refinance long-term debt maturing in 2017. On September 30, 2015, we modified the timing of the forecasted future issuance of fixed-rate debt in conjunction with the expected timing of the financing of the Humana Acquisition and, as a result, we de-designated these swaps and re-designated them as cash flow hedges against interest rate exposure related to the forecasted future issuance of fixed-rate debt. The effective portion of the hedge loss of $73 million pretax remains in accumulated other comprehensive loss, net of tax, and will be amortized as an increase to interest expense over the first 20 semi-annual interest payments related to the fixed-rate debt. At March 31, 2016, we performed a quarterly effectiveness test of these swaps and determined there was $4 million pretax of ineffectiveness. That ineffectiveness was recorded as a realized capital loss in the first quarter of 2016. In June 2016, we terminated the hedges in conjunction with the issuance of the 2016 senior notes and paid an aggregate of $103 million to the hedge counterparties upon termination. We performed a final effectiveness test upon termination of each interest rate swap and determined there was $2 million pretax of ineffectiveness. That ineffectiveness was recorded as a realized capital loss in the second quarter of 2016. The effective portion of the hedge loss of $25 million pretax was recorded in accumulated other comprehensive loss, net of tax. Upon the redemption of certain of the 2016 senior notes as described above, the remaining unamortized effective portion of the hedge loss recorded in accumulated other comprehensive income will be recognized in net income upon such redemption. Refer to Note 14 for additional information regarding hedge losses reclassified from accumulated other comprehensive loss to net income during the year ended December 31, 2016. Upon the redemption of certain of the 2016 senior notes in the first quarter of 2017, the remaining unamortized effective portion of the hedge loss as discussed above of approximately $330 million pretax recorded in accumulated other comprehensive income will be recognized in net income as a realized capital loss. Revolving Credit Facility On March 27, 2012, we entered into an unsecured $1.5 billion five-year revolving credit agreement (the “Credit Agreement”) with several financial institutions. On September 24, 2012, in connection with the acquisition of Coventry, we entered into a First Amendment (the “First Amendment”) to the Credit Agreement and also entered into an Incremental Commitment Agreement (the “Incremental Commitment Agreement”). On March 2, 2015, we entered into a Second Amendment to the Credit Agreement (the “Second Amendment”). On July 30, 2015, in connection with the Humana Acquisition, we entered into a Third Amendment (the “Third Amendment,” and together with the First Amendment, the Incremental Commitment Agreement, the Second Amendment and the Credit Agreement, resulting in the “Facility”). The Facility is an unsecured $2.0 billion revolving credit agreement. The Third Amendment modified the calculation of total debt for the purposes of determining compliance prior to the Closing Date (as defined below) with certain covenants to exclude debt incurred by us to finance the Humana Acquisition, the other financing transactions related to the Humana Acquisition and/or the payment of fees and expenses incurred in connection therewith so long as either (A) the net proceeds of such debt are set aside to finance the Humana Acquisition, the other financing transactions related to the Humana Acquisition and/or the payment of fees and expenses incurred in connection therewith or (B) such debt is subject to mandatory redemption in the event that the Merger Agreement is terminated or expires. In addition, upon our agreement with one or more financial institutions, we may expand the commitments under the Facility by an additional $500 million . The Facility also provides for the issuance of up to $200 million of letters of credit at our request, which count as usage of the available commitments under the Facility. In each of 2013, 2014 and 2015, we extended the maturity date of the Facility by one year. The maturity date of the Facility is March 27, 2020. Various interest rate options are available under the Facility. Any revolving borrowings mature on the termination date of the Facility. We pay facility fees on the Facility ranging from .050% to .150% per annum, depending upon our long-term senior unsecured debt rating. The facility fee was .100% at December 31, 2016 . The Facility contains a financial covenant that requires us to maintain a ratio of total debt to consolidated capitalization as of the end of each fiscal quarter at or below 50% . For this purpose, consolidated capitalization equals the sum of total shareholders’ equity, excluding any overfunded or underfunded status of our pension and OPEB plans and any net unrealized capital gains and losses, and total debt (as defined in the Facility). We met this requirement at December 31, 2016 . There were no amounts outstanding under the Facility at any time during the year ended December 31, 2016 or 2015 . Term Loan Agreement On July 30, 2015, in connection with the Humana Acquisition, we entered into a senior three-year $3.2 billion term loan credit agreement (the “Term Loan Agreement”) with a group of seventeen lenders. The lenders’ commitments under the Term Loan Agreement terminated on February 14, 2017, as a result of the termination of the Merger Agreement. Commercial Paper At December 31, 2016 and 2015, we did not have any commercial paper outstanding. Federal Home Loan Bank of Boston We are a member of the Federal Home Loan Bank of Boston (the “FHLBB”), and as a member we have the ability to obtain cash advances, subject to certain minimum collateral requirements. Our maximum borrowing capacity available from the FHLBB at December 31, 2016 was $854 million . At both December 31, 2016 and 2015, we did not have any outstanding borrowings from the FHLBB.

Pension and Other Postretiremen

Pension and Other Postretirement Plans	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Pension and Other Postretirement Plans	10. Pension and Other Postretirement Plans Defined Benefit Retirement Plans We sponsor various defined benefit plans, including two pension plans, and OPEB plans that provide certain health care and life insurance benefits for retired employees, including those of our former parent company. During 2016 , 2015 and 2014 we did not make any contribution to the Aetna Pension Plan. Effective December 31, 2010, our employees no longer earn future pension service credits in the Aetna Pension Plan (i.e., the Plan was “frozen” effective December 31, 2010), although the Aetna Pension Plan will continue to operate and account balances will continue to earn annual interest credits. In July 2014, we enhanced the Aetna Pension Plan. Effective December 1, 2014, we permitted certain current and future former employees with deferred vested Aetna Pension Plan balances to elect to receive a 100% lump-sum distribution. This election is a permanent addition to the Aetna Pension Plan. In addition, in July 2014, we announced a limited-time offer permitting certain former employees with deferred vested Aetna Pension Plan balances to elect a 100% lump-sum distribution. These distributions in 2014 were funded from existing Aetna Pension Plan assets and exceeded the total 2014 service and interest cost. As a result, we performed a remeasurement of the Aetna Pension Plan, and we recorded a pretax non-cash settlement charge of $112 million in 2014 in general and administrative expenses. We also sponsor a non-qualified supplemental pension plan (the “Non-qualified Pension Plan”) that, prior to January 1, 2007, had been used to provide benefits for wages above the Internal Revenue Code wage limits applicable to tax qualified pension plans (such as the Aetna Pension Plan). Effective January 1, 2007, no new benefits accrue under the Non-qualified Pension Plan, but interest will continue to be credited on outstanding supplemental cash balance accounts; and the plan may continue to be used to credit special pension arrangements. In addition, we currently provide certain medical and life insurance benefits for retired employees, including those of our former parent company. We provide subsidized health care benefits to certain eligible employees who terminated employment prior to December 31, 2006. There is a cap on our portion of the cost of providing medical and dental benefits to our retirees. Through December 31, 2015, all current and future retirees and employees who terminated employment at age 45 or later with at least five years of service were eligible to participate in our group health plans at their own cost. Effective January 1, 2016, only current and future retirees and employees who terminate employment at age 55 or later are eligible for such participation. The information set forth in the following tables is based upon current actuarial reports using the annual measurement dates (December 31, for each year presented) for our pension and OPEB plans. The following table shows the changes in the benefit obligations during 2016 and 2015 for our pension and OPEB plans: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Benefit obligation, beginning of year $ 5,946 $ 6,505 $ 257 $ 277 Interest cost 260 261 11 11 Actuarial loss (gain) 161 (453 ) — (10 ) Benefits paid (335 ) (367 ) (20 ) (21 ) Benefit obligation, end of year $ 6,032 $ 5,946 $ 248 $ 257 The pension plans’ benefit obligation remained relatively consistent in 2016 driven by interest cost recognized in 2016 and an increase in actuarial losses arising as a result of a lower discount rate as further described below; substantially offset by benefits paid in 2016. The Aetna Pension Plan comprises 96% of the pension plans’ total benefit obligation at December 31, 2016 . The discount rates used to determine the benefit obligation of our pension and OPEB plans were calculated using a yield curve as of our annual measurement date. Each yield curve consisted of a series of individual discount rates, with each discount rate corresponding to a single point in time, based on high-quality bonds. Projected benefit payments are discounted to the measurement date using the corresponding rate from the yield curve. The weighted average discount rate for our pension plans was 4.22% and 4.50% for 2016 and 2015 , respectively. The discount rate for our OPEB plans was 4.12% and 4.39% for 2016 and 2015 , respectively. The discount rates differ for our pension and OPEB plans due to the duration of the projected benefit payments for each plan. Beginning in 2017, we changed the approach used to estimate the interest cost component of net periodic benefit cost for pension and OPEB for plans that utilize a yield curve approach. Historically, we estimated the interest cost using a single weighted-average discount rate derived from the yield curve used to measure the projected benefit obligation. With this refinement, we will measure interest cost by applying the specific spot rates along that yield curve to the relevant projected cash flows for each component. We believe the new approach provides a more precise measurement of interest cost. This refinement has no effect on the measurement of our plan obligations. We have accounted for this as a change in accounting estimate and accordingly, have accounted for it on a prospective basis beginning in 2017. Additionally, based on the mortality experience of our pension and OPEB plans, in 2016 we utilized the RP-2014 Mortality Table with a generation projection of future mortality improvements using Scale MP-2016. In 2015 we utilized the RP-2014 Mortality Table with a generational projection of future mortality improvements using Scale MP-2015. In 2014 we utilized the RP-2014 Mortality Table with a generational projection of future mortality improvements using Scale MP-2014. The following table reconciles the beginning and ending balances of the fair value of plan assets during 2016 and 2015 for our pension and OPEB plans: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Fair value of plan assets, beginning of year $ 5,802 $ 6,147 $ 55 $ 58 Actual return on plan assets 426 — 1 1 Employer contributions 21 22 16 17 Benefits paid (335 ) (367 ) (20 ) (21 ) Fair value of plan assets, end of year $ 5,914 $ 5,802 $ 52 $ 55 The difference between the fair value of plan assets and the plan’s benefit obligation is referred to as the plan’s funded status. This funded status is an accounting-based calculation and is not indicative of our mandatory funding requirements. The funded status of our pension and OPEB plans at the measurement date for 2016 and 2015 was as follows: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Benefit obligation $ (6,032 ) $ (5,946 ) $ (248 ) $ (257 ) Fair value of plan assets 5,914 5,802 52 55 Funded status $ (118 ) $ (144 ) $ (196 ) $ (202 ) At December 31, 2016 , the fair value of plan assets of the Aetna Pension Plan was in excess of the benefit obligations, while the Non-qualified Pension Plan had benefit obligations in excess of the fair value of plan assets. Below is the funded status of each of our Pension Plans: Aetna Pension Plan Non-qualified Pension Plan (Millions) 2016 2015 2016 2015 Benefit obligation $ (5,807 ) $ (5,714 ) $ (225 ) $ (232 ) Fair value of plan assets 5,914 5,802 — — Funded status $ 107 $ 88 $ (225 ) $ (232 ) The amounts in accumulated other comprehensive loss that have not yet been recognized in net periodic benefit cost as of December 31, 2016 and 2015 were as follows: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Unrecognized prior service credit $ — $ (1 ) $ (19 ) $ (22 ) Unrecognized net actuarial losses 2,460 2,398 66 67 Amount recognized in accumulated other comprehensive loss $ (2,460 ) $ (2,397 ) $ (47 ) $ (45 ) The (liabilities) assets recognized on our balance sheets at December 31, 2016 and 2015 for our pension and OPEB plans were comprised of the following: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Accrued benefit assets reflected in other long-term assets $ 107 $ 88 $ — $ — Accrued benefit liabilities reflected in other current liabilities (20 ) (19 ) (13 ) (14 ) Accrued benefit liabilities reflected in other long-term liabilities (205 ) (213 ) (183 ) (188 ) Net amount of (liabilities) assets recognized at December 31, $ (118 ) $ (144 ) $ (196 ) $ (202 ) At December 31, 2016 , we had approximately $2.5 billion and $66 million of net actuarial losses for our pension and OPEB plans, respectively, and $19 million of prior service credits for our OPEB plans and an immaterial amount of prior service credits for our pension plan, that have not been recognized as components of net periodic benefit costs. We expect to recognize $65 million and $2 million in amortization of net actuarial losses for our pension and OPEB plans, respectively, and $4 million in amortization of prior service credits for our OPEB plans in 2017. Our amortization of prior service credits for our pension plans in 2017 is not expected to be material. Components of the net periodic benefit (income) cost of our defined benefit pension plans and OPEB plans for the years ended December 31, 2016 , 2015 and 2014 were as follows: Pension Plans OPEB Plans (Millions) 2016 2015 2014 2016 2015 2014 Amortization of prior service credit $ — $ (1 ) $ (1 ) $ (4 ) $ (4 ) $ (4 ) Interest cost 260 261 288 11 11 12 Expected return on plan assets (389 ) (419 ) (422 ) (3 ) (3 ) (3 ) Recognized net actuarial losses 61 62 47 3 3 1 Settlement charge — — 112 — — — Net periodic benefit (income) cost $ (68 ) $ (97 ) $ 24 $ 7 $ 7 $ 6 The weighted average assumptions used to determine net periodic benefit (income) cost in 2016 , 2015 and 2014 for the pension and OPEB plans were as follows: Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Discount rate 4.50 % 4.12 % 4.96 % 4.39 % 4.02 % 4.73 % Expected long-term return on plan assets 6.90 % 7.00 % 7.00 % 4.75 % 5.30 % 5.30 % We assume different health care cost trend rates for medical costs and prescription drug costs in estimating the expected costs of our OPEB plans. The assumed medical cost trend rate for 2017 is 5.5% , decreasing gradually to 4.5% by 2024. The assumed prescription drug cost trend rate for 2017 is 10.2% , decreasing gradually to 4.5% by 2024. These assumptions reflect our historical as well as expected future trends for retirees. In addition, the trend assumptions reflect factors specific to our retiree medical plan, such as plan design, cost-sharing provisions, benefits covered and the presence of subsidy caps. A one-percentage point increase in both the assumed medical cost and assumed prescription drug cost trend rates would result in a $.3 million pretax increase in the aggregate of the service and interest cost components of OPEB costs and a $8 million increase in the OPEB benefit obligation. A one-percentage point decrease in both the assumed medical cost and assumed prescription drug cost trend rates would result in a $.2 million pretax decrease in the aggregate of the service and interest cost components of OPEB costs and an $7 million decrease in the OPEB benefit obligation. Our current funding strategy for the Aetna Pension Plan is to fund an amount at least equal to the minimum funding requirement as determined under applicable regulatory requirements with consideration of factors such as the maximum tax deductibility of such amounts. Minimum funding requirements for the Aetna Pension Plan were met in 2016 and 2015 , and we were not required to make cash contributions for either of those years. We do not have any required contribution to the Aetna Pension Plan in 2017, although we may voluntarily contribute $60 million in 2017. Employer contributions related to the supplemental pension and OPEB plans represent payments to retirees for current benefits. We have no plans to return any pension or OPEB plan assets to the Company in 2017. Our non-qualified supplemental pension plan and OPEB plans do not have minimum funding requirements. Expected benefit payments, which reflect future employee service, as appropriate, of the pension and OPEB plans to be paid for each of the next five years and in the aggregate for the next five years thereafter at December 31, 2016 were as follows: (Millions) Pension Plans OPEB Plans 2017 $ 495 $ 18 2018 360 18 2019 360 18 2020 362 18 2021 366 17 2022-2026 1,844 82 Assets of the Aetna Pension Plan The assets of the Aetna Pension Plan (“Pension Assets”) primarily include debt and equity securities held in separate accounts, as well as common/collective trusts and real estate investments. The valuation methodologies used to price these debt and equity securities and common/collective trusts are similar to the methodologies described in Note 5 . Pension Assets also include investments in other assets that are carried at fair value. The following is a description of the valuation methodology used to price real estate investments and these additional investments, including the general classification pursuant to the valuation hierarchy. Real Estate - Real estate investments are valued by independent third party appraisers. The appraisals comply with the Uniform Standards of Professional Appraisal Practice, which includes, among other things, the income, cost, and sales comparison approaches to estimating property value. Therefore, these investments are classified in Level 3. Private equity limited partnerships - Private equity limited partnerships are carried at fair value which is estimated based on the fair value of the underlying investment funds provided by the general partner or manager of the investments, the financial statements of which generally are audited. We typically do not have a controlling ownership in our private equity limited partnership investments, and therefore we apply the equity method of accounting for these investments. Accordingly, these investments have been excluded from the fair value table below. Hedge fund limited partnerships - Hedge fund limited partnerships are carried at fair value which is estimated using the net asset value (“NAV”) per unit as reported by the administrator of the underlying investment fund as a practical expedient to fair value. Therefore, these investments have been excluded from the fair value table below. Pension Assets with changes in fair value measured on a recurring basis at December 31, 2016 were as follows: (Millions) Level 1 Level 2 Level 3 Total Debt securities: U.S. government securities $ 460 $ 122 $ — $ 582 States, municipalities and political subdivisions — 128 — 128 U.S. corporate securities — 1,291 — 1,291 Foreign securities — 103 — 103 Residential mortgage-backed securities — 163 — 163 Commercial mortgage-backed securities — 57 — 57 Other asset-backed securities — 60 — 60 Redeemable preferred securities — 6 — 6 Total debt securities 460 1,930 — 2,390 Equity securities: U.S. Domestic 1,305 5 — 1,310 International 611 — — 611 Domestic real estate 34 — — 34 Total equity securities 1,950 5 — 1,955 Other investments: Real estate — — 478 478 Common/collective trusts (1) — 465 — 465 Total other investments — 465 478 943 Total pension investments (2) $ 2,410 $ 2,400 $ 478 $ 5,288 (1) The assets in the underlying funds of common/collective trusts are comprised of $307 million of equity securities and $158 million of debt securities. (2) Excludes $180 million of cash and cash equivalents and other payables. Pension Assets with changes in fair value measured on a recurring basis at December 31, 2015 were as follows: (Millions) Level 1 Level 2 Level 3 Total Debt securities: U.S. government securities $ 428 $ 135 $ — $ 563 States, municipalities and political subdivisions — 126 — 126 U.S. corporate securities — 1,229 2 1,231 Foreign securities — 136 — 136 Residential mortgage-backed securities — 196 — 196 Commercial mortgage-backed securities — 51 1 52 Other asset-backed securities — 40 — 40 Redeemable preferred securities — 7 — 7 Total debt securities 428 1,920 3 2,351 Equity securities: U.S. Domestic 1,222 5 — 1,227 International 547 — — 547 Domestic real estate 28 — — 28 Total equity securities 1,797 5 — 1,802 Other investments: Real estate — — 497 497 Common/collective trusts (1) — 556 — 556 Total other investments — 556 497 1,053 Total pension investments (2) $ 2,225 $ 2,481 $ 500 $ 5,206 (1) The assets in the underlying funds of common/collective trusts are comprised of $302 million of equity securities and $254 million of debt securities. (2) Excludes $133 million of cash and cash equivalents and other payables. The changes in the balances of Level 3 Pension Assets during 2016 and 2015 were as follows: 2016 (Millions) Real Estate Other Total Beginning balance $ 497 $ 3 $ 500 Actual return on plan assets 42 — 42 Purchases, sales and settlements (61 ) (1 ) (62 ) Transfers out of Level 3 — (2 ) (2 ) Ending balance $ 478 $ — $ 478 2015 (Millions) Real Estate Other Total Beginning balance $ 470 $ 2 $ 472 Actual return on plan assets 46 — 46 Purchases, sales and settlements (19 ) — (19 ) Transfers into Level 3 — 1 1 Ending balance $ 497 $ 3 $ 500 The Aetna Pension Plan invests in a diversified mix of assets intended to maximize long-term returns while recognizing the need for adequate liquidity to meet ongoing benefit and administrative obligations. The risk of unexpected investment and actuarial outcomes is regularly evaluated. This evaluation is performed through forecasting and assessing ranges of investment outcomes over short- and long-term horizons, and by assessing the Aetna Pension Plan’s liability characteristics, our financial position and our future potential obligations from both the pension and general corporate perspectives. Complementary investment styles and techniques are utilized by multiple professional investment firms to further improve portfolio and operational risk characteristics. Public and private equity investments are used primarily to increase overall plan returns. Real estate investments are viewed favorably for their diversification benefits and above-average dividend generation. Fixed income investments provide diversification benefits and liability hedging attributes that are desirable, especially in falling interest rate environments. At December 31, 2016 , target investment allocations for the Aetna Pension Plan were: 38% in equity securities, 48% in debt securities, 7% in real estate, 4% in private equity limited partnerships and 3% in hedge funds. Actual asset allocations may differ from target allocations due to tactical decisions to overweight or underweight certain assets or as a result of normal fluctuations in asset values. Asset allocations are consistent with stated investment policies and, as a general rule, periodically rebalanced back to target asset allocations. Asset allocations and investment performance are formally reviewed periodically throughout the year by the plan’s Benefit Finance Committee. Forecasting of asset and liability growth is performed at least annually. We have several benefit plans for retired employees currently supported by the OPEB plan assets. OPEB plan assets are directly and indirectly invested in a diversified mix of traditional asset classes, primarily high-quality fixed income securities. The actual and target asset allocations of the OPEB plans used at December 31, 2016 and 2015 presented as a percentage of total plan assets, were as follows: Target Target (Millions) 2016 Allocation 2015 Allocation Equity securities 11 % 5-15% 10 % 5-15% Debt securities 82 % 80-90% 83 % 80-90% Real estate/other 7 % 0-10% 7 % 0-10% Our expected return on plan assets assumption is based on many factors, including forecasted capital market real returns over a long-term horizon, forecasted inflation rates, historical compounded asset returns and patterns and correlations on those returns. Expectations for modest increases in interest rates, normal inflation trends and average capital market real returns led us to an expected return on the pension plan assets assumption of 6.90% for 2016 and 7.00% for each of 2015 and 2014 , and an expected return on OPEB plan assets assumption of 4.75% for 2016 and 5.30% for 2015 and 2014 . We regularly review actual asset allocations and periodically rebalance our investments to the mid-point of our targeted allocation ranges when we consider it appropriate. 401(k) Plan Our employees are eligible to participate in a defined contribution retirement savings plan under which designated contributions may be invested in our common stock or certain other investments (the “Aetna 401(k) Plan”). Our 401(k) contribution to the Aetna 401(k) Plan provides for a match of 100% of up to 6% of the eligible pay contributed by the employee. During 2016 , 2015 and 2014 , we made $197 million , $198 million and $180 million , respectively, in aggregate of matching contributions to our 401(k) plans. The matching contributions are made in cash and invested according to each participant’s investment elections. The plan trustee held 7 million shares of our common stock for plan participants at December 31, 2016 . At December 31, 2016 , 34 million shares of our common stock were reserved for issuance under the Aetna 401(k) Plan.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes The components of our income tax provision in 2016 , 2015 and 2014 were as follows: (Millions) 2016 2015 2014 Current taxes: Federal $ 1,662 $ 1,797 $ 1,233 State 129 112 84 Total current taxes 1,791 1,909 1,317 Deferred taxes (benefits): Federal (55 ) (59 ) 114 State (1 ) (9 ) 24 Total deferred income taxes (56 ) (68 ) 138 Total income taxes $ 1,735 $ 1,841 $ 1,455 Income taxes were different from the amount computed by applying the statutory federal income tax rate to income before income taxes as follows: 2016 2015 2014 (Millions) Amount Percent Amount Percent Amount Percent Amount at statutory rate $ 1,397 35.0 % $ 1,483 35.0 % $ 1,225 35.0 % Health insurer fee 293 7.3 % 300 7.1 % 212 6.1 % State income taxes 83 2.1 % 63 1.5 % 78 2.2 % Other, net (38 ) (.9 )% (5 ) (.1 )% (60 ) (1.7 )% Income taxes $ 1,735 43.5 % $ 1,841 43.5 % $ 1,455 41.6 % The significant components of our net deferred tax liabilities at December 31, 2016 and 2015 were as follows: (Millions) 2016 2015 Deferred tax assets: Insurance reserves $ 231 $ 302 Reserve for anticipated future losses on discontinued products 225 268 Employee and postretirement benefits 196 220 Net operating losses 147 165 Severance and facilities 135 18 Investments, net 80 92 Debt fair value adjustments 23 33 Deferred revenue 21 21 Other 117 66 Gross deferred tax assets 1,175 1,185 Less: Valuation allowance 118 128 Deferred tax assets, net of valuation allowance 1,057 1,057 Deferred tax liabilities: Goodwill and other acquired intangible assets 814 863 Cumulative depreciation and amortization 185 231 Unrealized gains on investment securities 42 138 Other 20 2 Total gross deferred tax liabilities 1,061 1,234 Net deferred tax liabilities $ (4 ) $ (177 ) Valuation allowances are provided when we estimate that it is more likely than not that deferred tax assets will not be realized. A valuation allowance has been established primarily related to state net operating losses. We base our estimates of the future realization of deferred tax assets primarily on historic taxable income and existing deferred tax liabilities. We participate in the Compliance Assurance Process (the “CAP”) with the Internal Revenue Service (the “IRS”). Under the CAP, the IRS undertakes audit procedures during the tax year and as the return is prepared for filing. The IRS has concluded its CAP audit of our 2015 tax return as well as all the prior years. We expect the IRS will conclude its CAP audit of our 2016 tax return in 2017. We are also subject to audits by various state taxing authorities for tax years from 2000 through 2015. We believe we carry appropriate reserves for any exposure to state tax issues. At both December 31, 2016 and December 31, 2015 we did not have material uncertain tax positions reflected in our consolidated balance sheets.

Stock-based Employee Incentive

Stock-based Employee Incentive Plans	12 Months Ended
	Dec. 31, 2016
Stock-based Employee Incentive Plans [Abstract]
Stock-based Employee Incentive Plans	12. Stock-based Employee Incentive Plans Our stock-based employee compensation plans (collectively, the “Plans”) provide for awards of stock options, SARs, PSARs, restricted stock units RSUs, MSUs, PSUs, deferred contingent common stock and the ability for employees to purchase common stock at a discount. At December 31, 2016 , 23 million common shares were available for issuance under the Plans. Executive, middle management and non-management employees may be granted stock options, SARs, PSARs, RSUs, MSUs and PSUs, each of which are described below: Stock Options, SARs and PSARs We have not granted stock options since 2005, and no stock options were outstanding as of December 31, 2016. Stock options were granted to purchase our common stock at or above the market price on the date of grant. SARs granted will be settled in stock, net of taxes, based on the appreciation of our stock price on the exercise date over the market price on the date of grant. SARs and stock options generally become 100% vested three years after the grant is made, with one-third vesting each year. Vested SARs and stock options may be exercised at any time during the ten years after grant, except in certain circumstances, generally related to employment termination or retirement. At the end of the ten -year period, any unexercised SARs and stock options expire. The SARs granted to certain employees during 2016 and 2015 and described above had an estimated grant date fair value per SAR of $34.33 and $32.13 , respectively. The grant date fair value was calculated using a modified Black-Scholes option pricing model using the following assumptions: 2016 2015 Expected term (in years) 7.11 6.48 Volatility 32.9 % 33.4 % Risk-free interest rate 1.52 % 1.81 % Dividend yield 0.91 % 1.13 % Initial price $ 103.45 $ 100.50 The expected term is based on historical equity award activity. Volatility is based on a weighted average of the historical volatility of our stock price and implied volatility from traded options on our stock. The risk-free interest rate is based on a U.S. Treasury rate with a life equal to the expected life of the SARs grant. This rate was calculated by interpolating between the 7-year and 10-year U.S. Treasury rates for 2016 SARs grants and the 5-year and 10-year U.S. Treasury rates for 2015 SARs grants. The dividend yield is based on our historical dividends declared in the 12 months prior to the grant date. PSARs represent the opportunity to vest in SARs. For the PSARs granted in 2013 (“2013 PSARs”), the number of vested PSARs (which could range in specified increments from zero to 700,000 SARs) was dependent on Aetna’s total shareholder return over a three year performance period relative to a defined peer group of companies. The 2013 PSARs were subject to a three-year vesting period that ended on August 5, 2016, and vested at 500,000 SARs. We estimated the grant date fair value of the 2013 PSARs using a Monte Carlo simulation. The 2013 PSARs had a grant date per PSAR fair value of $18.64 . That grant date fair value was calculated using the following assumptions: Expected settlement period (in years) 6.12 Volatility 40.4 % Risk-free interest rate .6 % Dividend yield 1.25 % Initial price $ 64.25 The stock option, SAR and PSAR transactions during 2016 , 2015 and 2014 were as follows: (Millions, except exercise price and remaining life) Number of Stock Options, SARs and PSARs Weighted Average Exercise Price Weighted Average Remaining Contractual Life Aggregate Intrinsic Value 2014 Outstanding, beginning of year 10.5 $ 43.27 3.5 $ 265 Granted 1.4 72.36 — — Exercised (3.7 ) 40.50 — 132 Expired or forfeited (.1 ) 46.94 — — Outstanding, end of year ( 1) 8.1 $ 49.37 4.2 $ 318 Exercisable, end of year 6.1 $ 42.86 2.6 $ 280 2015 Outstanding, beginning of year 8.1 $ 49.37 4.2 $ 318 Granted 2.0 101.41 — — Exercised (2.5 ) 43.90 — 155 Expired or forfeited (.2 ) 91.25 — — Outstanding, end of year ( 1) 7.4 $ 64.11 5.3 $ 325 Exercisable, end of year 4.1 $ 45.88 2.6 $ 252 2016 Outstanding, beginning of year 7.4 $ 64.11 5.3 $ 325 Granted 2.4 104.47 — — Exercised (1.4 ) 52.99 — 85 Expired or forfeited (.4 ) 83.25 — — Outstanding, end of year 8.0 $ 77.20 5.9 $ 373 Exercisable, end of year 4.3 $ 57.26 3.6 $ 287 (1) PSARs are included in this table in 2015 and 2014 at the maximum amount that could potentially vest. The following is a summary of information regarding SARs outstanding at December 31, 2016 (millions, except remaining contractual life and exercise price): Outstanding Exercisable Range of Exercise Prices Number Outstanding Weighted Average Remaining Contractual Life (Years) Weighted Average Exercise Price Aggregate Intrinsic Value Number Exercisable Weighted Average Exercise Price Aggregate Intrinsic Value 20.00-30.00 (1) — 2.4 $ 24.97 $ 2 — $ 24.97 $ 2 30.00-40.00 1.1 2.1 32.11 98 1.1 32.11 98 40.00-50.00 .7 .4 45.55 53 .7 45.55 53 50.00-60.00 .8 1.1 50.70 59 .8 50.70 59 60.00-70.00 .5 6.6 64.25 30 .5 64.25 30 70.00-80.00 1.0 6.8 72.34 50 .6 72.34 31 100.00-110.00 3.6 8.6 102.36 79 .6 101.05 14 110.00-120.00 .3 9.2 115.29 2 — — — $20.00-$130.00 (2) 8.0 5.9 $ 77.20 $ 373 4.3 $ 57.26 $ 287 (1) The number of outstanding and exercisable SARs and PSARs with exercise prices between $20 and $30 rounded to zero. (2) The number of outstanding SARs with exercise prices between $80 and $100 and between $120 and $130 rounded to zero . During 2016 , 2015 and 2014 , the following activity occurred under the Plans: (Millions) 2016 2015 2014 Cash received from stock option exercises $ — $ 7 $ 32 Intrinsic value of stock options/SARs exercised and stock units vested 384 413 323 Tax benefits realized for the tax deductions from stock options and SARs exercised and stock units vested 77 101 87 Fair value of stock options, SARs, PSARs and stock units vested (1) 223 126 107 (1) The fair value represents the aggregate grant date fair value of the stock options, SARs, PSARs and stock units as of the respective grant dates. We settle our SARs and stock units with newly-issued common stock and generally utilized the proceeds from stock options to repurchase our common stock in the open market in the same period. RSUs, MSUs and PSUs For each RSU granted, employees receive one share of common stock, net of taxes, at the end of the vesting period. RSUs generally become 100% vested approximately three years from the grant date, with one-third vesting each December. The grant date fair value is determined based on the market price of our common stock on the date of grant. The number of vested MSUs (which could range from zero to 150% of the original number of units granted) is dependent on the weighted average closing price of our common stock for the thirty trading days prior to the vesting date, including the vesting date. Each vested MSU represents one share of common stock and will be paid in shares of common stock, net of taxes. MSUs representing 50% of the grant date fair value of the MSUs granted in 2012 were subject to a two -year vesting period while the remaining MSUs granted in 2012 were subject to a three -year vesting period. MSUs granted in 2014 and 2013 are subject to a three -year vesting period. There were no MSUs granted in 2016 or 2015. The number of vested PSUs (which could range from zero to 200% of the original number of units granted) is dependent upon the degree to which we achieve performance goals, which for the most part, are set at the time of grant as determined by our Board’s Committee on Compensation and Talent Management (the “Compensation Committee”). Each vested PSU represents one share of common stock and will be paid in shares of common stock, net of taxes. The grant date fair value is determined based on the market price of our common stock on the date of grant. Below is a summary of the performance period and vesting percentages for each tranche of PSUs granted by the Company: • PSUs granted in 2013 (“2013 PSUs”): Certain PSUs granted in 2013 were subject to a single three-year performance period that ended on December 31, 2015, and vested at 74.61% of the original number of units granted. Certain PSUs granted in 2013 were subject to a two -year vesting period with two separate performance periods. Half of these PSUs were subject to a one-year performance period that ended on December 31, 2013, and vested at 127.08% of the original number of units granted. The remaining half were subject to a one-year performance period that ended on December 31, 2014, and vested at 131.62% of the original number of units granted. • PSUs granted in 2014 (“2014 PSUs”): The 2014 PSUs had a two-year performance period that ended on December 31, 2015, and vested at 200% of the original number of units granted. The 2014 PSUs are subject to a three -year vesting period. • PSUs granted in 2015 (“2015 PSUs”): The 2015 PSUs have a three-year performance period that will end on December 31, 2017, and are subject to a three -year vesting period. • PSUs granted in 2016 (“2016 PSUs”): The 2016 PSUs have a three-year performance period that will end on December 31, 2018, and are subject to a three -year vesting period From 2010 through 2014, we granted MSUs to certain employees. We did not grant any MSUs in 2015 or 2016. We estimate the grant date fair value of MSUs using a Monte Carlo simulation. MSUs granted in 2014 had a weighted average per MSU grant date fair value of $74.99 . The weighted-average per MSU grant date fair value was calculated using the following assumptions: 2014 Volatility 26.4 % Risk-free interest rate .7 % Dividend yield 1.3 % Initial price $ 72.26 The annualized volatility of the price of our common stock was calculated over the three-year period preceding the grant date of the MSUs. The risk-free interest rates for periods within the expected life of the MSUs were based on a constant maturity yield curve in effect on the grant date of the MSUs. The dividend yield assumption was based on our expected 2014 annual dividend payout. RSU, MSU and PSU transactions in 2016 , 2015 and 2014 were as follows (number of units in millions): 2016 2015 2014 RSUs, MSUs and PSUs Weighted Average Grant Date Fair Value RSUs, MSUs and PSUs Weighted Average Grant Date Fair Value RSUs, MSUs and PSUs Weighted Average Grant Date Fair Value RSUs, MSUs and PSUs at beginning of year 3.9 $ 73.40 5.1 $ 58.57 5.3 $ 48.82 Granted 2.1 98.60 1.8 100.52 2.7 71.88 Vested (2.7 ) 68.87 (2.6 ) 59.72 (2.5 ) 50.11 Forfeited (.4 ) 71.17 (.4 ) 70.94 (.4 ) 56.89 RSUs, MSUs and PSUs at end of year 2.9 $ 91.95 3.9 $ 73.40 5.1 $ 58.57 Stock Compensation Expense In 2016 , 2015 and 2014 we recorded share-based compensation expense of $191 million , $181 million and $163 million , respectively, in general and administrative expenses. We also recorded related tax benefits of $33 million in 2016 and $37 million in both 2015 and 2014 , respectively. At December 31, 2016 , $185 million of total unrecognized compensation costs related to SARs is expected to be recognized over a weighted-average period of 1.7 years.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2016
Class of Stock Disclosures [Abstract]
Capital Stock	13. Shareholders’ Equity Share Repurchases From time to time, our Board authorizes us to repurchase our common stock. The repurchases are effected from time to time in the open market, through negotiated transactions, including accelerated share repurchase agreements, and through plans designed to comply with Rule 10b5-1 under the Securities Exchange Act of 1934, as amended. The activity under Board authorized share repurchase programs in 2016 , 2015 and 2014 was as follows: Purchase Not to Exceed Shares Purchased 2016 2015 2014 (Millions) Shares Cost Shares Cost Shares Cost Authorization date: November 21, 2014 $ 1,000 — $ — — $ — — $ — February 28, 2014 1,000 — — 3.0 296 7.6 621 September 27, 2013 750 — — — — 8.3 597 Total repurchases N/A — $ — 3.0 $ 296 15.9 $ 1,218 Repurchase authorization remaining at December 31, N/A $ 1,083 N/A $ 1,083 N/A $ 1,379 As described above, from time to time we enter into accelerated share repurchase agreements with unrelated third party financial institutions. The number of shares repurchased under each agreement is based on the volume-weighted average price of our common stock during the purchase period. We completed the following accelerated share repurchase programs with repurchase periods during the years ended December 31, 2016 and 2015: Trade Date: Value of Repurchase Program (Millions) Repurchase Period Number of Shares Repurchased (Millions) March 2, 2015 $ 100.0 April 2015 0.9 On February 17, 2017, our Board approved a new share repurchase program that authorized us to repurchase up to $4.0 billion of our common stock. Dividends Prior to termination of the Merger Agreement, Aetna was not permitted to declare, set aside or pay any dividend or other distribution other than a regular quarterly cash dividend in the ordinary course of business, which could not exceed $.25 per share. In addition, the Term Loan Agreement contained a covenant limiting “Restricted Payments” (as defined in the Term Loan Agreement) by Aetna, subject to certain exceptions and baskets, including an exception permitting the payment of regular cash dividends. Our dividend policy following termination of the Merger Agreement will be determined by our Board. Declaration and payment of future dividends is at the discretion of our Board and may be adjusted as business needs or marketplace conditions change. In 2016 and 2015 our Board declared the following cash dividends: Date Declared Dividend Amount Per Share Stockholders of Record Date Date Paid/ To be Paid Total Dividends (Millions) Year ended December 31, 2015 February 27, 2015 $ .25 April 9, 2015 April 24, 2015 $ 87 May 15, 2015 .25 July 16, 2015 July 31, 2015 87 September 25, 2015 .25 October 15, 2015 October 30, 2015 87 December 4, 2015 .25 January 14, 2016 January 29, 2016 87 Year ended December 31, 2016 February 19, 2016 $ .25 April 14, 2016 April 29, 2016 88 May 20, 2016 .25 July 14, 2016 July 29, 2016 88 September 30, 2016 .25 October 13, 2016 October 28, 2016 88 December 2, 2016 .25 January 12, 2017 January 27, 2017 88 On February 17, 2017, our Board declared a cash dividend of $.50 per share that will be paid on April 28, 2017 to shareholders of record at the close of business on April 13, 2017. Preferred Stock and Undesignated Shares In addition to the common stock disclosed on our balance sheets, 8 million shares of Class A voting preferred stock, $.01 par value per share, have been authorized and none are issued or outstanding at December 31, 2016 . At December 31, 2016 , there were also 442 million undesignated shares that our Board has the power to divide into such classes and series, with such voting rights, designations, preferences, limitations and special rights as our Board determines. Regulatory Requirements Our business operations are conducted through subsidiaries that principally consist of HMOs and insurance companies. Our HMO and insurance subsidiaries report their financial statements in accordance with accounting practices prescribed by state regulatory authorities which may differ from GAAP. The combined statutory net income for the years ended and combined statutory capital and surplus at December 31, 2016 , 2015 and 2014 for our insurance and HMO subsidiaries were as follows: (Millions) 2016 2015 2014 Statutory net income $ 2,229 $ 2,186 $ 2,127 Statutory capital and surplus 10,413 9,883 9,406 During 2016 , our insurance and HMO subsidiaries paid approximately $2.3 billion of dividends to the Company. In addition to general state law restrictions on payments of dividends and other distributions to shareholders applicable to all corporations, HMOs and insurance companies are subject to further regulations that, among other things, may require those companies to maintain certain levels of equity and restrict the amount of dividends and other distributions that may be paid to their equity holders. At December 31, 2016, these amounts were as follows: (Millions) Minimum statutory surplus required by regulators $ 3,738 Investments on deposit with regulatory bodies 561 Maximum dividend distributions permitted in 2016 without state approval 1,902

Other Comprehensive (Loss) Inco

Other Comprehensive (Loss) Income	12 Months Ended
	Dec. 31, 2016
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive (Loss) Income	14. Other Comprehensive (Loss) Income Shareholders’ equity included the following activity in accumulated other comprehensive loss in 2016 , 2015 and 2014 : At December 31, (Millions) 2016 2015 2014 Previously impaired debt securities: (1) Beginning of period balance $ 19 $ 35 $ 34 Net unrealized (losses) gains ($(31), $(69) and $1 pretax) (20 ) (45 ) 1 Less: Net reclassification of (losses) gains to earnings ($(26) and $(44)) (2) (17 ) (29 ) — Other comprehensive (loss) income (3 ) (16 ) 1 End of period balance 16 19 35 All other securities: Beginning of period balance 312 568 327 Net unrealized (losses) gains ($(12), $(490) and $365 pretax) (8 ) (318 ) 237 Less: Net reclassification of gains (losses) to earnings ($11, $(97) and $(7) pretax) (2) 7 (62 ) (4 ) Other comprehensive (loss) income (15 ) (256 ) 241 End of period balance 297 312 568 Derivatives and foreign currency: Beginning of period balance (74 ) $ (61 ) $ — Net unrealized losses ($(273), $(26) and $(90) pretax) (177 ) (17 ) (58 ) Less: Net reclassification of (losses) gains to earnings ($(25), $(6) and $4 pretax) (3) (16 ) (4 ) 3 Other comprehensive loss (161 ) (13 ) (61 ) End of period balance (235 ) (74 ) (61 ) Pension and OPEB plans: Beginning of period balance (1,587 ) (1,653 ) (1,273 ) Net unrealized net actuarial (losses) gains arising during the period ($(126), $41 and $(739) pretax) (82 ) 27 (481 ) Less: Net pension settlement charge ($(112) pretax) (4) — — (73 ) Less: Net amortization of net actuarial losses ($(64), $(64) and $(48) pretax) (4) (42 ) (42 ) (31 ) Less: Net amortization of prior service credit ($5, $4 and $4 pretax) (4) 3 3 3 Other comprehensive (loss) income (43 ) 66 (380 ) End of period balance (1,630 ) (1,587 ) (1,653 ) Total beginning of period accumulated other comprehensive loss (1,330 ) (1,111 ) (912 ) Total other comprehensive loss (222 ) (219 ) (199 ) Total end of period accumulated other comprehensive loss $ (1,552 ) $ (1,330 ) $ (1,111 ) (1) Represents specifically identified unrealized gains on the non-credit related component of impaired debt securities that we do not intend to sell and subsequent changes in the fair value of any previously impaired security. (2) Reclassifications out of accumulated other comprehensive income for specifically identified previously impaired debt securities and all other securities are reflected in net realized capital gains (losses) within the Consolidated Statements of Income. (3) Reclassifications out of accumulated other comprehensive income for specifically identified foreign currency gains (losses) and derivatives are reflected in net realized capital gains (losses) within the Consolidated Statements of Income, except for the specifically identified effective portion of derivatives related to interest rate swaps which are reflected in interest expense. Refer to Note 9 for additional information. (4) Reclassifications out of accumulated other comprehensive income for specifically identified pension and OPEB plan expenses are reflected in general and administrative expenses within the Consolidated Statements of Income. During 2014, our reclassifications out of accumulated other comprehensive income for the Aetna Pension Plan reflect a pension settlement charge of $73 million ( $112 million pretax). (Refer to Note 10 for additional information).

Earnings Per Common Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Earnings Per Common Share	15. Earnings Per Common Share Basic earnings per common share (“EPS”) is computed by dividing net income attributable to Aetna by the weighted-average number of common shares outstanding during the reporting period. Diluted EPS is computed in a similar manner, except that the weighted average number of common shares outstanding is adjusted for the dilutive effects of our outstanding stock-based compensation awards, but only if the effect is dilutive. The computations of basic and diluted EPS for 2016 , 2015 and 2014 are as follows: (Millions, except per common share data) 2016 2015 2014 Net income attributable to Aetna $ 2,271 $ 2,390 $ 2,041 Weighted average shares used to compute basic EPS 351.3 349.3 355.5 Dilutive effect of outstanding stock-based compensation awards 3.0 3.3 3.6 Weighted average shares used to compute diluted EPS 354.3 352.6 359.1 Basic EPS $ 6.46 $ 6.84 $ 5.74 Diluted EPS $ 6.41 $ 6.78 $ 5.68 The stock-based compensation awards excluded from the calculation of diluted EPS for 2016 , 2015 and 2014 are as follows: (Millions) 2016 2015 2014 Stock appreciation rights ("SARs") (1) .1 .5 .3 Other stock-based compensation awards (2) .7 .8 1.2 (1) SARs are excluded from the calculation of diluted EPS if the exercise price is greater than the average market price of Aetna common shares during the period (i.e., the awards are anti-dilutive). (2) Performance stock units ("PSUs"), certain market stock units ("MSUs") with performance conditions, and performance stock appreciation rights ("PSARs") are excluded from the calculation of diluted EPS if all necessary performance conditions have not been satisfied at the end of the reporting period (refer to Note 12 for additional information about PSARs). All outstanding stock options were included in the calculation of diluted EPS for 2014 . There were no stock options outstanding at December 31, 2016 or 2015.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Reinsurance	16. Reinsurance We utilize reinsurance agreements primarily to reduce our required capital and to facilitate the acquisition or disposition of certain insurance contracts. Ceded reinsurance agreements permit us to recover a portion of our losses from reinsurers, although they do not discharge our primary liability as the direct insurer of the risks reinsured. Effective October 1, 1998, we reinsured certain policyholder liabilities and obligations related to individual life insurance in conjunction with our former parent company’s sale of this business. These transactions were in the form of indemnity reinsurance arrangements, whereby the assuming companies contractually assumed certain policyholder liabilities and obligations, although we remain directly obligated to policyholders. The liability related to our obligation is recorded in future policy benefits and policyholders’ funds on our balance sheets. Assets related to and supporting these policies were transferred to the assuming companies, and we recorded a reinsurance recoverable. Effective 2013 to 2016, we entered into certain three to five -year reinsurance agreements with unrelated reinsurers that allowed us to reduce our required capital and provided collateralized excess of loss reinsurance coverage on a portion of our group Commercial Insured Health Care business. In January 2017, we entered into two four -year reinsurance agreements with an unrelated reinsurer that allowed us to reduce our required capital and provided collateralized excess of loss reinsurance coverage on a portion of our group Commercial Insured Health Care business. The ACA established a temporary reinsurance program that expired at the end of 2016. Under this program, all issuers of major medical commercial insurance products and self-insured plan sponsors were required to contribute funding in amounts set by HHS. Funds collected were utilized to reimburse issuers’ high claims costs incurred for qualified individual members. The expense related to this required funding is reflected in general and administrative expenses for all of our insurance products with the exception of products associated with qualified individual members; this expense for qualified individual members is reflected as a reduction of premium revenue. When annual claim costs incurred by our qualified individual members exceed a specified attachment point, we are entitled to certain reimbursements from this program. We record a receivable and offset health care costs to reflect our estimate of these recoveries. Refer to Note 2 for additional information about the ACA’s temporary three-year reinsurance program. Reinsurance recoverables recorded at December 31, 2016 and 2015 were as follows: (Millions) Total Recoverables Reinsurer 2016 2015 Lincoln Life & Annuity Company of New York $ 444 $ 458 VOYA Retirement Insurance and Annuity Company 209 223 Affordable Care Act 202 395 All Other 164 138 Total $ 1,019 $ 1,214 Direct, assumed and ceded health care premiums earned for the years ended December 31 were as follows: (Millions) 2016 2015 2014 Direct $ 54,062 $ 51,539 $ 49,497 Assumed 402 368 316 Ceded (348 ) (289 ) (251 ) Net health care premiums $ 54,116 $ 51,618 $ 49,562 The impact of reinsurance on health care costs for the years ended December 31 were as follows: (Millions) 2016 2015 2014 Direct $ 44,341 $ 42,038 $ 40,980 Assumed 339 298 263 Ceded (425 ) (624 ) (496 ) Net health care costs $ 44,255 $ 41,712 $ 40,747 Assumed and ceded other premiums and current and future benefit expense related to our Group Insurance and Large Case Pensions segments were not material during the years ended 2016 , 2015 or 2014 . There is not a material difference between premiums on a written basis versus an earned basis. We also have various agreements with unrelated reinsurers that do not qualify for reinsurance accounting under GAAP, and consequently are accounted for using deposit accounting. We entered into these contracts to reduce the risk of catastrophic loss which in turn reduces our capital and surplus requirements surrounding certain portions of our group term life, group accidental death and dismemberment, Medicare Advantage and group Commercial Insured Health Care businesses. Total deposit assets and liabilities related to reinsurance agreements that do not quality for reinsurance accounting under GAAP were not material as of December 31, 2016 or 2015.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	17. Commitments and Contingencies Guarantees We have the following significant guarantee and indemnification arrangements at December 31, 2016 . • ASC Claim Funding Accounts - We have arrangements with certain banks for the processing of claim payments for our ASC customers. The banks maintain accounts to fund claims of our ASC customers. The customer is responsible for funding the amount paid by the bank each day. In these arrangements, we guarantee that the banks will not sustain losses if the responsible ASC customer does not properly fund its account. The aggregate maximum exposure under these arrangements is generally limited to $250 million . We can limit our exposure to this guarantee by suspending the payment of claims for ASC customers that have not adequately funded the amount paid by the bank. • Indemnification Agreements - In connection with certain acquisitions and dispositions of assets and/or businesses, our various issuances of long-term debt and certain of our reinsurance agreements, we have incurred certain customary indemnification obligations to the applicable seller, purchaser, underwriters and/or various other participants. In general, we have agreed to indemnify the other party for certain losses relating to the assets or business that we or they purchased or sold or for other matters on terms that are customary for similar transactions. Certain portions of our indemnification obligations are capped at the applicable transaction price, while other arrangements are not subject to such a limit. At December 31, 2016 , we do not believe that our future obligations under any of these agreements will be material to our financial position. • Separate Accounts assets - Certain Separate Accounts assets associated with the Large Case Pensions business represent funds maintained as a contractual requirement to fund specific pension annuities that we have guaranteed. Minimum contractual obligations underlying the guaranteed benefits in these Separate Accounts were approximately $1.8 billion and $2.0 billion at December 31, 2016 and 2015 , respectively. Refer to Note 2 for additional information on Separate Accounts. Contract holders assume all investment and mortality risk and are required to maintain Separate Account balances at or above a specified level. The level of required funds is a function of the risk underlying the Separate Account’s investment strategy. If contract holders do not maintain the required level of Separate Account assets to meet the annuity guarantees, we would establish an additional liability. Contract holders’ balances in the Separate Accounts at December 31, 2016 exceeded the value of the guaranteed benefit obligation. As a result, we were not required to maintain any additional liability for our related guarantees at December 31, 2016 . • Minimum Volume Commitments - In connection with the Coventry acquisition we assumed certain supplier agreements with minimum volume commitments which require us to make payments to the suppliers if the level of medical membership subject to the agreements falls below specified levels. The maximum potential amount of future payments we could be required to make over the remaining terms of the agreements, assuming the medical membership subject to the agreements is zero, is $24 million . Guaranty Fund Assessments, Market Stabilization and Other Non-Voluntary Risk Sharing Pools Under guaranty fund laws existing in all states, insurers doing business in those states can be assessed (in most states up to prescribed limits) for certain obligations of insolvent insurance companies to policyholders and claimants. The life and health insurance guaranty associations in which we participate that operate under these laws respond to insolvencies of long-term care insurers as well as health insurers. Our assessments generally are based on a formula relating to our health care premiums in the state compared to the premiums of other insurers. Certain states allow assessments to be recovered over time as offsets to premium taxes. Some states have similar laws relating to HMOs and/or other payors such as not-for-profit consumer-governed health plans established under the ACA. In 2009, the Pennsylvania Insurance Commissioner (the “Commissioner”) placed long-term care insurer Penn Treaty Network America Insurance Company and one of its subsidiaries (collectively, “Penn Treaty”) in rehabilitation, an intermediate action before insolvency, and subsequently petitioned a state court to convert the rehabilitation into a liquidation. In 2012, the state court denied the Commissioner’s petition for liquidation. The Pennsylvania Supreme Court affirmed that ruling in July 2015. Between April 2013 and October 2014, the Commissioner filed proposed rehabilitation plans, which have been withdrawn. In July 2016, the Commissioner again petitioned the state court to convert the rehabilitation into a liquidation. A hearing to consider that petition was held in late 2016. If Penn Treaty is placed in liquidation, we and other insurers likely would be assessed immediately and/or over a period of years by guaranty associations for the payments the guaranty associations are required to make to Penn Treaty policyholders. We anticipate that Penn Treaty will be placed in liquidation in the first half of 2017. If Penn Treaty is placed in liquidation in the first half of 2017, we expect to record an estimated liability and expense of approximately $230 million pretax at the time of such event. It is reasonably possible that in the future we may record a liability and expense relating to other insolvencies which could have a material adverse effect on our operating results, financial position and cash flows. While historically we have ultimately recovered more than half of guaranty fund assessments through statutorily permitted premium tax offsets, significant increases in assessments could lead to legislative and/or regulatory actions that may limit future offsets. HMOs in certain states in which we do business are subject to assessments, including market stabilization and other risk-sharing pools, for which we are assessed charges based on incurred claims, demographic membership mix and other factors. We establish liabilities for these assessments based on applicable laws and regulations. In certain states, the ultimate assessments we pay are dependent upon our experience relative to other entities subject to the assessment, and the ultimate liability is not known at the balance sheet date. While the ultimate amount of the assessment is dependent upon the experience of all pool participants, we believe we have adequate reserves to cover such assessments. Terminated Acquisition of Humana and Related Matters On February 14, 2017, Aetna and Molina entered into the APA Termination Agreement pursuant to which Aetna terminated the Molina APA, including all schedules and exhibits thereto, and all ancillary agreements contemplated thereby or entered pursuant thereto. Under the APA Termination Agreement, among other things, Aetna agreed to pay Molina in cash approximately 70% of Molina’s transaction costs. We expect to pay Molina the applicable transaction costs during the first quarter of 2017. In June 2016, we issued $13.0 billion of 2016 senior notes to partially fund the Humana Acquisition. In accordance with the terms of the 2016 senior notes, on February 14, 2017, we issued a notice of redemption for the entire $10.2 billion aggregate principal amount of the Special Mandatory Redemption Notes at a redemption price equal to 101% of the aggregate principal amount of those notes plus accrued and unpaid interest. We will redeem the Special Mandatory Redemption Notes on or about March 16, 2017. As a result of the redemption of the Special Mandatory Redemption Notes, in the first quarter of 2017, we will recognize on a pretax basis in our net income the entire approximately $420 million unamortized portion of the related cash flow hedge losses, debt issuance costs and debt issuance discounts and the entire approximately $100 million redemption premium paid on the Special Mandatory Redemption Notes upon such redemption. Litigation and Regulatory Proceedings Humana Acquisition - Department of Justice Litigation On July 21, 2016, the DOJ and certain state attorneys general filed a civil complaint in the U.S. District Court for the District of Columbia (the “District Court”) against us and Humana charging that the Humana Acquisition would violate Section 7 of the Clayton Antitrust Act, and seeking a permanent injunction to prevent Aetna from acquiring Humana. On January 23, 2017, the District Court granted the DOJ’s request to enjoin the Humana Acquisition. Out-of-Network Benefit Proceedings We are named as a defendant in several purported class actions and individual lawsuits arising out of our practices related to the payment of claims for services rendered to our members by health care providers with whom we do not have a contract (“out-of-network providers”). Among other things, these lawsuits allege that we paid too little to our health plan members and/or providers for these services, among other reasons, because of our use of data provided by Ingenix, Inc., a subsidiary of one of our competitors (“Ingenix”). Other major health insurers are the subject of similar litigation or have settled similar litigation. Various plaintiffs who are health care providers or medical associations seek to represent nationwide classes of out-of-network providers who provided services to our members during the period from 2001 to the present. Various plaintiffs who are members in our health plans seek to represent nationwide classes of our members who received services from out-of-network providers during the period from 2001 to the present. Taken together, these lawsuits allege that we violated state law, the Employee Retirement Income Security Act of 1974, as amended (“ERISA”), the Racketeer Influenced and Corrupt Organizations Act (“RICO”) and federal antitrust laws, either acting alone or in concert with our competitors. The purported classes seek reimbursement of all unpaid benefits, recalculation and repayment of deductible and coinsurance amounts, unspecified damages and treble damages, statutory penalties, injunctive and declaratory relief, plus interest, costs and attorneys’ fees, and seek to disqualify us from acting as a fiduciary of any benefit plan that is subject to ERISA. Individual lawsuits that generally contain similar allegations and seek similar relief have been brought by health plan members and out-of-network providers. The first class action case was commenced on July 30, 2007. The federal Judicial Panel on Multi-District Litigation (the “MDL Panel”) has consolidated these class action cases in the U.S. District Court for the District of New Jersey (the “New Jersey District Court”) under the caption In re: Aetna UCR Litigation, MDL No. 2020 (“MDL 2020”). In addition, the MDL Panel has transferred the individual lawsuits to MDL 2020. On May 9, 2011, the New Jersey District Court dismissed the physician plaintiffs from MDL 2020 without prejudice. The New Jersey District Court’s action followed a ruling by the United States District Court for the Southern District of Florida (the “Florida District Court”) that the physician plaintiffs were enjoined from participating in MDL 2020 due to a prior settlement and release. The United States Court of Appeals for the Eleventh Circuit has dismissed the physician plaintiffs’ appeal of the Florida District Court’s ruling. On December 6, 2012, we entered into an agreement to settle MDL 2020. Under the terms of the proposed nationwide settlement, we would have been released from claims relating to our out-of-network reimbursement practices from the beginning of the applicable settlement class period through August 30, 2013. The settlement agreement did not contain an admission of wrongdoing. The medical associations were not parties to the settlement agreement. Under the settlement agreement, we would have paid up to $120 million to fund claims submitted by health plan members and health care providers who were members of the settlement classes. These payments also would have funded the legal fees of plaintiffs’ counsel and the costs of administering the settlement. In connection with the proposed settlement, the Company recorded an after-tax charge to net income attributable to Aetna of $78 million in the fourth quarter of 2012. The settlement agreement provided us the right to terminate the agreement under certain conditions related to settlement class members who opted out of the settlement. Based on a report provided to the parties by the settlement administrator, the conditions permitting us to terminate the settlement agreement were satisfied. On March 13, 2014, we notified the New Jersey District Court and plaintiffs’ counsel that we were terminating the settlement agreement. Various legal and factual developments since the date of the settlement agreement led us to believe terminating the settlement agreement was in our best interests. As a result of this termination, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced first quarter 2014 other general and administrative expenses by $103 million pretax. On June 30, 2015, the New Jersey District Court granted in part our motion to dismiss the proceeding. The New Jersey District Court dismissed with prejudice the plaintiffs’ RICO and federal antitrust claims; their ERISA claims that are based on our disclosures and our purported breach of fiduciary duties; and certain of their state law claims. The New Jersey District Court also dismissed with prejudice all claims asserted by several medical association plaintiffs. The plaintiffs’ remaining claims are for ERISA benefits and breach of contract. We intend to defend ourselves vigorously against the plaintiffs’ remaining claims. We also have received subpoenas and/or requests for documents and other information from, and been investigated by, attorneys general and other state and/or federal regulators, legislators and agencies relating to, and we are involved in other litigation regarding, our out-of-network benefit payment and administration practices. It is reasonably possible that others could initiate additional litigation or additional regulatory action against us with respect to our out-of-network benefit payment and/or administration practices. CMS Actions CMS regularly audits our performance to determine our compliance with CMS’s regulations and our contracts with CMS and to assess the quality of services we provide to Medicare beneficiaries. CMS uses various payment mechanisms to allocate and adjust premium payments to our and other companies’ Medicare plans by considering the applicable health status of Medicare members as supported by information prepared, maintained and provided by health care providers. We collect claim and encounter data from providers and generally rely on providers to appropriately code their submissions to us and document their medical records, including the diagnosis data submitted to us with claims. CMS pays increased premiums to Medicare Advantage plans and prescription drug program plans for members who have certain medical conditions identified with specific diagnosis codes. Federal regulators review and audit the providers’ medical records to determine whether those records support the related diagnosis codes that determine the members’ health status and the resulting risk-adjusted premium payments to us. In that regard, CMS has instituted risk adjustment data validation (“RADV”) audits of various Medicare Advantage plans, including certain of the Company’s plans, to validate coding practices and supporting medical record documentation maintained by health care providers and the resulting risk adjusted premium payments to the plans. CMS may require us to refund premium payments if our risk adjusted premiums are not properly supported by medical record data. The Office of Inspector General (the “OIG”) also is auditing risk adjustment data of other companies, and we expect CMS and the OIG to continue auditing risk adjustment data. CMS revised its audit methodology for RADV audits to determine refunds payable by Medicare Advantage plans for contract year 2011 and forward. Under the revised methodology, among other things, CMS will project the error rate identified in the audit sample of approximately 200 members to all risk adjusted premium payments made under the contract being audited. Historically, CMS did not project sample error rates to the entire contract. As a result, the revised methodology may increase our exposure to premium refunds to CMS based on incomplete medical records maintained by providers. Since 2013, CMS has selected certain of our Medicare Advantage contracts for various contract years for RADV audit. We are currently unable to predict which of our Medicare Advantage contracts will be selected for future audit, the amounts of any retroactive refunds of, or prospective adjustments to, Medicare Advantage premium payments made to us, the effect of any such refunds or adjustments on the actuarial soundness of our Medicare Advantage bids, or whether any RADV audit findings would cause a change to our method of estimating future premium revenue in future bid submissions to CMS or compromise premium assumptions made in our bids for prior contract years or the current contract year. Any premium or fee refunds or adjustments resulting from regulatory audits, whether as a result of RADV, Public Exchange related or other audits by CMS, the OIG, HHS or otherwise, including audits of our minimum medical loss ratio rebates, methodology and/or reports, could be material and could adversely affect our operating results, financial position and cash flows. Other Litigation and Regulatory Proceedings We are involved in numerous other lawsuits arising, for the most part, in the ordinary course of our business operations, including claims of or relating to bad faith, medical malpractice, non-compliance with state and federal regulatory regimes, marketing misconduct, failure to timely or appropriately pay or administer claims and benefits in our Health Care and Group Insurance businesses (including our post-payment audit and collection practices and reductions in payments to providers due to sequestration), provider network structure (including the use of performance-based networks and termination of provider contracts), provider directory accuracy, rescission of insurance coverage, improper disclosure of personal information, anticompetitive practices, patent infringement and other intellectual property litigation, other legal proceedings in our Health Care and Group Insurance businesses and employment litigation. Some of these other lawsuits are or are purported to be class actions. We intend to defend ourselves vigorously against the claims brought in these matters. Awards to us and others of certain government contracts, particularly Medicaid contracts and contracts with government customers in our Commercial business, are subject to increasingly frequent protests by unsuccessful bidders. These protests may result in awards to us being reversed, delayed or modified. The loss or delay in implementation of any government contract could adversely affect our operating results. We will continue to defend vigorously contract awards we receive. In addition, our operations, current and past business practices, current and past contracts, and accounts and other books and records are subject to routine, regular and special investigations, audits, examinations and reviews by, and from time to time we receive subpoenas and other requests for information from, CMS, the U.S. Department of Health and Human Services, various state insurance and health care regulatory authorities, state attorneys general, treasurers and offices of inspector general, the Center for Consumer Information and Insurance Oversight, OIG, the Office of Personnel Management, the U.S. Department of Labor, the U.S. Department of the Treasury, the U.S. Food and Drug Administration, committees, subcommittees and members of the U.S. Congress, the U.S. Department of Justice, the Federal Trade Commission, U.S. attorneys and other state, federal and international governmental authorities. These government actions include inquiries by, and testimony before, certain members, committees and subcommittees of the U.S. Congress regarding our withdrawal from certain states’ Public Exchanges for 2017, certain of our current and past business practices, including our overall claims processing and payment practices, our business practices with respect to our small group products, student health products or individual customers (such as market withdrawals, rating information, premium increases and medical benefit ratios), executive compensation matters and travel and entertainment expenses, as well as the investigations by, and subpoenas and requests from, attorneys general and others described above under “Out-of-Network Benefit Proceedings.” A significant number of states are investigating life insurers’ claims payment and related escheat practices. These investigations have resulted in significant charges to earnings by other life insurers in connection with related settlements. We have received requests for information from a number of states, and certain of our subsidiaries are being audited, with respect to our life insurance claim payment and related escheat practices. In the fourth quarter of 2013, we made changes to our life insurance claim payment practices (including related escheatment practices) based on evolving industry practices and regulatory expectations and interpretations, including expanding our existing use of the Social Security Administration’s Death Master File to identify additional potentially unclaimed death benefits and locate applicable beneficiaries. As a result of these changes, in the fourth quarter of 2013, we increased our estimated liability for unpaid life insurance claims with respect to insureds who passed away on or before December 31, 2013, and recorded in current and future benefits a charge of $36 million ( $55 million pretax). Given the judicial, legislative and regulatory uncertainty with respect to life insurance claim payment and related escheat practices, it is reasonably possible that we may incur additional liability related to those practices, whether as a result of further changes in our business practices, litigation, government actions or otherwise, which could adversely affect our operating results and cash flows. There also continues to be a heightened level of review and/or audit by regulatory authorities of, and increased litigation regarding, our and the rest of the health care and related benefits industry’s business and reporting practices, including premium rate increases, utilization management, development and application of medical policies, complaint, grievance and appeal processing, information privacy, provider network structure (including provider network adequacy, the use of performance-based networks and termination of provider contracts), provider directory accuracy, calculation of minimum medical loss ratios and/or payment of related rebates, delegated arrangements, rescission of insurance coverage, limited benefit health products, student health products, pharmacy benefit management practices (including the use of narrow networks and the placement of drugs in formulary tiers), sales practices, customer service practices, vendor oversight and claim payment practices (including payments to out-of-network providers and payments on life insurance policies). As a leading national health and related benefits company, we regularly are the subject of government actions of the types described above. These government actions may prevent or delay us from implementing planned premium rate increases and may result, and have resulted, in restrictions on our business, changes to or clarifications of our business practices, retroactive adjustments to premiums, refunds or other payments to members, beneficiaries, states or the federal government, withholding of premium payments to us by government agencies, assessments of damages, civil or criminal fines or penalties, or other sanctions, including the possible suspension or loss of licensure and/or suspension or exclusion from participation in government programs. Estimating the probable losses or a range of probable losses resulting from litigation, government actions and other legal proceedings is inherently difficult and requires an extensive degree of judgment, particularly where the matters involve indeterminate claims for monetary damages, involve claims for injunctive relief, may involve fines, penalties or punitive damages that are discretionary in amount, involve a large number of claimants or regulatory authorities, represent a change in regulatory policy, present novel legal theories, are in the early stages of the proceedings, are subject to appeal or could result in changes in business practices. In addition, because most legal proceedings are resolved over long periods of time, potential losses are subject to change due to, among other things, new developments, changes in litigation strategy, the outcome of intermediate procedural and substantive rulings and other parties’ settlement posture and their evaluation of the strength or weakness of their case against us. Except as specifically noted above under “Other Litigation and Regulatory Proceedings,” we are currently unable to predict the ultimate outcome of, or reasonably estimate the losses or a range of losses resulting from, the matters described above under “Litigation and Regulation Proceedings”, and it is reasonably possible that their outcome could be material to us. Other Obligations We have operating leases for office space and certain computer and other equipment. Rental expenses for these items were $167 million , $165 million and $177 million in 2016 , 2015 and 2014 , respectively. For 2017 through 2021, our future net minimum payments under non-cancelable leases and funding obligations relating to equity limited partnership investments, commercial mortgage loans and real estate partnerships were as following: (Millions) 2017 2018 2019 2020 2021 Future net minimum payments under non-cancelable leases $ 143 $ 121 $ 81 $ 47 $ 37 Funding requirements for equity limited partnership investments, commercial mortgage loans and real estate partnerships 177 127 94 56 37 Total $ 320 $ 248 $ 175 $ 103 $ 74

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segment Information	18. Segment Information Our operations are conducted in three business segments: Health Care, Group Insurance and Large Case Pensions. Our Corporate Financing segment is not a business segment; it is added to our business segments to reconcile to our consolidated results. The Corporate Financing segment includes interest expense on our outstanding debt and the financing components of our pension and OPEB plan expense (the prior service cost components of this expense are allocated to our business segments). Non-GAAP financial measures we disclose, such as operating earnings, should not be considered a substitute for, or superior to, financial measures determined or calculated in accordance with GAAP. Summarized financial information of our segment operations (1) for 2016 , 2015 and 2014 were as follows: (Millions) Health Care Group Insurance Large Case Pensions Corporate Financing Total Company 2016 Revenue from external customers $ 59,860 $ 2,251 $ 48 $ — $ 62,159 Net investment income 458 226 226 — 910 Interest expense — — — 604 604 Depreciation and amortization expense 681 — — — 681 Income taxes (benefits) 1,856 26 44 (191 ) 1,735 Operating earnings (loss) (2) 2,948 124 14 (169 ) 2,917 2015 Revenue from external customers $ 57,203 $ 2,240 $ 42 $ — $ 59,485 Net investment income 408 238 271 — 917 Interest expense — — — 369 369 Depreciation and amortization expense 671 — — — 671 Income taxes (benefits) 1,908 38 (9 ) (96 ) 1,841 Operating earnings (loss) (2) 2,712 136 17 (148 ) 2,717 2014 Revenue from external customers $ 54,677 $ 2,214 $ 86 $ — $ 56,977 Net investment income 368 261 317 — 946 Interest expense — — — 334 334 Depreciation and amortization expense 627 2 — — 629 Income taxes (benefits) 1,587 57 1 (190 ) 1,455 Operating earnings (loss) (2) 2,377 171 21 (164 ) 2,405 (1) Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer. (2) Operating earnings (loss) excludes net realized capital gains or losses, amortization of other acquired intangible assets and the other items described in this Note 18. A reconciliation of net income attributable to Aetna to operating earnings (1) in 2016 , 2015 and 2014 was as follows. (Millions) 2016 2015 2014 Net income attributable to Aetna $ 2,271 $ 2,390 $ 2,041 Transaction and integration-related costs 517 258 201 Restructuring costs 404 15 — Reduction of reserve for anticipated future losses on discontinued products (128 ) — — Litigation-related proceeds — (110 ) — Loss on early extinguishment of long-term debt — — 181 Pension settlement charge — — 112 Release of litigation-related reserve — — (103 ) Amortization of other acquired intangible assets 247 255 243 Net realized capital (gain) losses (86 ) 65 (80 ) Income tax benefit (308 ) (156 ) (190 ) Operating earnings $ 2,917 $ 2,717 $ 2,405 (1) In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance: • We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. • Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses. • In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products. • In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income. • In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes. • During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. • In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement. • The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings. Revenues from external customers by product in 2016 , 2015 and 2014 were as follows: (Millions) 2016 2015 2014 Health care premiums $ 54,116 $ 51,618 $ 49,562 Health care fees and other revenue 5,744 5,585 5,115 Group insurance premiums 2,143 2,139 2,110 Group insurance fees and other revenues 108 101 104 Large case pensions premiums 39 32 76 Large case pensions other revenue 9 10 10 Total revenue from external customers (1) (2) $ 62,159 $ 59,485 $ 56,977 (1) All within the U.S., except approximately $642 million , $1.3 billion and $1.2 billion in 2016 , 2015 and 2014 , respectively, which were derived from foreign customers. (2) Revenue from the U.S. federal government was approximately $20.5 billion , $17.8 billion and $16.5 billion in 2016 , 2015 and 2014 , respectively, in the Health Care and Group Insurance segments. These amounts exceeded 10 percent of our total revenue from external customers in each of 2016 , 2015 and 2014 . The following is a reconciliation of revenue from external customers to total revenues included in our statements of income in 2016 , 2015 and 2014 : (Millions) 2016 2015 2014 Revenue from external customers $ 62,159 $ 59,485 $ 56,977 Net investment income 910 917 946 Net realized capital gains (losses) 86 (65 ) 80 Total revenue $ 63,155 $ 60,337 $ 58,003 Long-lived assets, which are principally within the U.S., were $579 million and $622 million at December 31, 2016 and 2015 , respectively.

Discontinued Products

Discontinued Products	12 Months Ended
	Dec. 31, 2016
Discontinued Products [Abstract]
Discontinued Products	19. Discontinued Products Prior to 1993, we sold single-premium annuities (“SPAs”) and guaranteed investment contracts (“GICs”), primarily to employer sponsored pension plans. In 1993, we discontinued selling these products to Large Case Pensions customers, and now we refer to these products as discontinued products. In November 2016, the last outstanding GIC matured. We discontinued selling these products because they were generating losses for us, and we projected that they would continue to generate losses over their life (which is currently greater than 30 years for SPAs); so we established a reserve for anticipated future losses at the time of discontinuance. This reserve represents the present value (at the risk-free rate of return consistent with the duration of the liabilities) of the difference between the expected cash flows from the assets supporting these products and the cash flows expected to be required to meet the obligations of the outstanding contracts. Key assumptions in setting the reserve for anticipated future losses include future investment results, payments to retirees, mortality and retirement rates and the cost of asset management and customer service. In 2014, we modified the mortality tables used in order to reflect the more up-to-date 2014 Retired Pensioner’s Mortality table. The mortality tables were previously modified in 2012, in order to reflect the more up-to-date 2000 Retired Pensioner’s Mortality table, and in 1995, in order to reflect the more up-to-date 1994 Uninsured Pensioner’s Mortality table. In 1997, we began the use of a bond default assumption to reflect historical default experience. Other than these changes, since 1993 there have been no significant changes to the assumptions underlying the reserve. We review the adequacy of this reserve quarterly based on actual experience. As long as our expected future losses remain consistent with prior projections, the results of the discontinued products are applied against the reserve and do not impact net income attributable to Aetna. If actual or expected future losses are greater than we currently estimate, we may increase the reserve, which could adversely impact net income attributable to Aetna. If actual or expected future losses are less than we currently estimate, we may decrease the reserve, which could favorably impact net income attributable to Aetna. As a result of this review, $84 million ( $128 million pretax) of the reserve was released during 2016. This reserve release was primarily due to favorable retirement experience as well as favorable investment performance compared to assumptions we previously made in estimating the reserve. The reserve at each of December 31, 2016 and 2015 reflects management’s best estimate of anticipated future losses, and is included in future policy benefits on our balance sheet. The activity in the reserve for anticipated future losses on discontinued products in 2016 , 2015 and 2014 was as follows (pretax): (Millions) 2016 2015 2014 Reserve, beginning of period $ 1,067 $ 1,015 $ 980 Operating (loss) income (34 ) (9 ) 6 Net realized capital gains 57 61 29 Reserve reduction (128 ) — — Reserve, end of period $ 962 $ 1,067 $ 1,015 During 2016, our discontinued products reflected operating losses and net realized capital gains, primarily attributable to gains from the sale of debt securities. During 2015, our discontinued products reflected operating losses and net realized capital gains, primarily attributable to gains from the sale of other invested assets and investment real estate. During 2014, our discontinued products reflected operating income and net realized capital gains, primarily attributable to gains from the sale of debt securities. We evaluated these 2016 results against the expectations of future cash flows assumed in estimating the reserve for anticipated future losses and do not believe that an adjustment to the reserve was required at December 31, 2016 . The anticipated run-off of the discontinued products reserve balance at December 31, 2016 (assuming that assets are held until maturity and that the reserve run-off is proportional to the liability run-off) is as follows: (Millions) 2017 $ 54 2018 53 2019 51 2020 50 2021 48 Thereafter 706 Assets and liabilities supporting discontinued products (1) at December 31, 2016 and 2015 were as follows: (Millions) 2016 2015 Assets: Debt and equity securities available for sale $ 1,913 $ 2,020 Mortgage loans 370 396 Other investments 646 643 Total investments 2,929 3,059 Other assets 104 129 Current and deferred income taxes — 21 Receivable from continuing products (2) 554 602 Total assets $ 3,587 $ 3,811 Liabilities: Future policy benefits $ 2,326 $ 2,494 Reserve for anticipated future losses on discontinued products 962 1,067 Current and deferred income taxes 42 — Other liabilities (3) 257 250 Total liabilities $ 3,587 $ 3,811 (1) Assets supporting the discontinued products are distinguished from assets supporting continuing products. (2) At the time of discontinuance, a receivable from Large Case Pensions’ continuing products was established on the discontinued products balance sheet. This receivable represented the net present value of anticipated cash shortfalls in the discontinued products, which will be funded from continuing products. Interest on the receivable is accrued at the discount rate that was used to calculate the reserve. The offsetting payable, on which interest is similarly accrued, is reflected in continuing products. Interest on the payable generally offsets investment income on the assets available to fund the shortfall. These amounts are eliminated in consolidation. (3) Net unrealized capital gains on the available-for-sale debt securities are included in other liabilities and are not reflected in consolidated shareholders’ equity. The discontinued products investment portfolio has changed since inception. Mortgage loans have decreased from $5.4 billion ( 37% of the investment portfolio) at December 31, 1993 to $370 million ( 13% of the investment portfolio) at December 31, 2016 . This was a result of maturities, prepayments and the securitization and sale of commercial mortgages. Also, real estate decreased from $500 million ( 4% of the investment portfolio) at December 31, 1993 to $108 million ( 4% of the investment portfolio) at December 31, 2016 , primarily as a result of sales. The resulting proceeds were primarily reinvested in debt securities, equity securities and other investments. Over time, the then-existing mortgage loan and real estate portfolios and the reinvested proceeds have resulted in greater investment returns than we originally assumed in 1993. At December 31, 2016 , the expected run-off of the SPA liabilities, including future interest, was as follows: (Millions) 2017 $ 348 2018 332 2019 316 2020 301 2021 285 Thereafter 3,540 The liability expected as of December 31, 1993 and the actual liability balances at December 31, 2016 , 2015 and 2014 for the GIC and SPA liabilities were as follows: Expected Actual (Millions) GIC SPA GIC SPA 2014 $ 12 $ 2,281 $ — $ 2,646 2015 10 2,112 — 2,494 2016 9 1,942 — 2,326 The GIC balances were lower than expected in each period because several contract holders redeemed their contracts prior to contract maturity. In November 2016, the last outstanding GIC matured. The SPA balances in each period were higher than expected because of additional amounts received under existing contracts. The distributions on our discontinued products consisted of scheduled contract maturities, settlements and benefit payments of $364 million , $356 million and $378 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. Participant-directed withdrawals from our discontinued products were not significant in the years ended December 31, 2016 , 2015 or 2014 . Cash required to fund these distributions was provided by earnings and scheduled payments on, and sales of, invested assets.

Quarterly Financial Data

Quarterly Financial Data	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	Quarterly Data (unaudited) (Millions, except per share and common stock data) First Second Third Fourth 2016 Total revenue $ 15,694 $ 15,952 $ 15,782 $ 15,727 Income before income taxes $ 1,289 $ 1,354 $ 1,073 $ 275 Income taxes (551 ) (561 ) (476 ) (147 ) Net income including non-controlling interests 738 793 597 128 Less: Net (loss) income attributable to non-controlling interests 1 2 (7 ) (11 ) Net income attributable to Aetna $ 737 $ 791 $ 604 $ 139 Net income attributable to Aetna per share - basic (1) $ 2.10 $ 2.25 $ 1.72 $ .40 Net income attributable to Aetna per share - diluted (1) 2.09 2.23 1.70 .39 2015 Total revenue $ 15,094 $ 15,241 $ 14,953 $ 15,049 Income before income taxes $ 1,366 $ 1,262 $ 1,023 $ 585 Income taxes (590 ) (527 ) (461 ) (263 ) Net income including non-controlling interests 776 735 562 322 Less: Net income (loss) attributable to non-controlling interests (1 ) 3 2 1 Net income attributable to Aetna $ 777 $ 732 $ 560 $ 321 Net income attributable to Aetna per share - basic (1) $ 2.22 $ 2.10 $ 1.60 $ .92 Net income attributable to Aetna per share - diluted (1) 2.20 2.08 1.59 .91 (1) Calculation of net income attributable to Aetna per share is based on weighted average shares outstanding during each quarter and, accordingly, the sum may not equal the total for the year.

Summary of Significant Accoun28

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Principles of Consolidation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) and include the accounts of Aetna and the subsidiaries that we control. All significant intercompany balances have been eliminated in consolidation. The Company has evaluated subsequent events from the balance sheet date through the date the financial statements were issued and determined there were no subsequent events to disclose other than as disclosed in Notes 3, 9, 13, 16 and 17.
Reclassification Policy	Reclassifications Certain prior year amounts have been reclassified to conform to the current year presentation.
Use of Estimates Policy	Use of Estimates The preparation of the accompanying consolidated financial statements in conformity with GAAP requires the use of estimates and assumptions that affect the amounts reported in these consolidated financial statements and notes. We consider the following accounting estimates critical in the preparation of the accompanying consolidated financial statements: health care costs payable, other insurance liabilities, recoverability of goodwill and other acquired intangible assets, measurement of defined benefit pension and other postretirement employee benefit plans, other-than-temporary impairment of debt securities, revenue recognition, allowance for estimated terminations and uncollectible accounts and accounting for certain provisions of the Patient Protection and Affordable Care Act and the Health Care and Education Reconciliation Act of 2010 (as amended, collectively, the “ACA”). We use information available to us at the time estimates are made; however, these estimates could change materially if different information or assumptions were used. Additionally, these estimates may not ultimately reflect the actual amounts of the final transactions that occur.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include cash on-hand and debt securities with an original maturity of three months or less when purchased. The carrying value of cash equivalents approximates fair value due to the short-term nature of these investments. Cash and cash equivalents at December 31, 2016 include approximately $13 billion of highly-rated money market fund investments related to the net proceeds received from the 2016 senior notes we issued in June 2016 to partially fund our then pending acquisition of Humana Inc. (the “Humana Acquisition”). These money market funds have average maturities of 60 days or less and are redeemable daily at par value plus accrued dividends with specified yield rates.
Investments	Investments Debt and Equity Securities Debt and equity securities consist primarily of U.S. Treasury and agency securities, mortgage-backed securities, corporate and foreign bonds and other debt and equity securities. Debt securities are classified as either current or long-term investments based on their contractual maturities unless we intend to sell an investment within the next twelve months, in which case it is classified as current on our balance sheets. We have classified our debt and equity securities as available for sale and carry them at fair value. Refer to Note 5 for additional information on how we estimate the fair value of these investments. The cost for mortgage-backed and other asset-backed securities is adjusted for unamortized premiums and discounts, which are amortized using the interest method over the estimated remaining term of the securities, adjusted for anticipated prepayments. We regularly review our debt and equity securities to determine whether a decline in fair value below the carrying value is other-than-temporary. When a debt or equity security is in an unrealized capital loss position, we monitor the duration and severity of the loss to determine if sufficient market recovery can occur within a reasonable period of time. If a decline in the fair value of a debt security is considered other-than-temporary, the cost basis or carrying value of the debt security is written down. The write-down is then bifurcated into its credit and non-credit related components. The amount of the credit-related component is included in our operating results, and the amount of the non-credit related component is included in other comprehensive income, unless we intend to sell the debt security or it is more likely than not that we will be required to sell the debt security prior to its anticipated recovery of its amortized cost basis. We do not accrue interest on debt securities when management believes the collection of interest is unlikely. If we intend to sell an equity security, we will recognize the unrealized capital gain or loss in our operating results. Mortgage Loans We value our mortgage loan investments on our balance sheet at the unpaid principal balance, net of impairment reserves. A mortgage loan may be impaired when it is a problem loan (i.e., more than 60 days delinquent, in bankruptcy or in process of foreclosure), a potential problem loan (i.e., high probability of default) or a restructured loan. For impaired loans, a specific impairment reserve is established for the difference between the recorded investment in the loan and the estimated fair value of the collateral. We apply our loan impairment policy individually to all loans in our portfolio. The impairment evaluation described above also considers characteristics and risk factors attributable to the aggregate portfolio. We establish an additional allowance for loan losses if it is probable that there will be a credit loss on a group of similar mortgage loans. We consider the following characteristics and risk factors when evaluating if a credit loss is probable on a group of similar mortgage loans: loan to value ratios, property type (e.g., office, retail, apartment, industrial), geographic location, vacancy rates and property condition. As a result of that evaluation, we determined that a credit loss was not probable and did not record any additional allowance for groups of similar mortgage loans in 2016 , 2015 or 2014 . We record full or partial impairments of loans at the time an event occurs affecting the legal status of the loan, typically at the time of foreclosure or upon a loan modification giving rise to forgiveness of debt. Interest income on a potential problem loan or restructured loan is accrued to the extent we deem it collectible and the loan continues to perform under its original or restructured terms. Interest income on problem loans is recognized on a cash basis. Cash payments on loans in the process of foreclosure are treated as a return of principal. Mortgage loans with a maturity date or a committed prepayment date within twelve months are classified as current on our balance sheets. Other Investments Other investments consist primarily of the following: • Private equity and hedge fund limited partnerships, which are carried at fair value on our balance sheets. The fair values of private equity limited partnerships are estimated based on the fair value of the underlying investment funds provided by the general partner or manager of the investments, the financial statements of which generally are audited. We typically do not have a controlling ownership in our private equity limited partnership investments, and therefore we apply the equity method of accounting for these investments. Hedge fund limited partnerships are carried at fair value which is estimated using the net asset value (“NAV”) per unit as reported by the administrator of the underlying investment fund as a practical expedient to fair value. We review our investments for impairment at least quarterly and monitor their performance throughout the year through discussions with the administrators, managers and/or general partners. If we become aware of an impairment of a limited partnership's investments through our review or prior to receiving the limited partnership's financial statements at the balance sheet date, we will recognize an impairment by recording a reduction in the carrying value of the limited partnership with a corresponding charge to realized capital losses. • Investment real estate, which is carried on our balance sheets at depreciated cost, including capital additions, net of write-downs for other-than-temporary declines in fair value. Depreciation is calculated using the straight-line method based on the estimated useful life of each asset. If any of our real estate investments is considered held-for-sale, we carry it at the lower of its carrying value or fair value less estimated selling costs. We generally estimate fair value using a discounted future cash flow analysis in conjunction with comparable sales information. At the time of the sale, we record the difference between the sales price and the carrying value as a realized capital gain or loss. • Privately-placed equity securities, which are carried at cost on our balance sheets. We do not estimate the fair value of these securities if there are no identified events or changes in circumstances that may have a significant adverse effect on the fair value of the investment. Additionally, as a member of the Federal Home Loan Bank of Boston (“FHLBB”), we are required to purchase and hold shares of the FHLBB. These shares are restricted and also carried at cost. • Bank loans, which are carried on our balance sheets at amortized cost, net of any allowance for impairments. If any of our bank loans are considered held-for-sale, we carry those loans at the lower of cost or fair value. • Derivatives, which we make limited use of in order to manage interest rate, foreign exchange and price risk and credit exposure. The derivatives we use consist primarily of interest rate swaps, treasury rate locks, forward contracts, futures contracts, warrants, put options, and credit default swaps. Derivative assets are recorded in investments and derivative liabilities are recorded in accrued expenses and other current liabilities on our balance sheets and reflected at fair value. When we enter into a derivative contract, if certain criteria are met, we may designate it as one of the following: a hedge of the fair value of a recognized asset or liability or of an unrecognized firm commitment; a hedge of a forecasted transaction or of the variability of cash flows to be received or paid related to a recognized asset or liability; or a foreign currency fair value or cash flow hedge.
Net Investment Income And Realized Capital Gains And Losses	Net Investment Income Net investment income on investments supporting Health Care and Group Insurance liabilities and Large Case Pensions products (other than experience-rated and discontinued products) is reflected in our operating results. Experience-rated products are products in the Large Case Pensions business where the contract holder, not us, assumes investment and other risks, subject to, among other things, minimum guarantees provided by us. The effect of investment performance on experience-rated products is allocated to contract holders’ accounts daily, based on the underlying investment experience and, therefore, does not impact our operating results (as long as our minimum guarantees are not triggered). When we discontinued the sale of our fully-guaranteed Large Case Pensions products, we established a reserve for anticipated future losses from these discontinued products and segregated the related investments. Investment performance on this separate portfolio is ultimately credited/charged to the reserve and, generally, does not impact our operating results. Net investment income supporting Large Case Pensions’ experience-rated and discontinued products is included in net investment income in our statements of income and is credited to contract holders’ accounts or the reserve for anticipated future losses through a charge to current and future benefits. Realized/Unrealized Capital Gains and Losses Realized capital gains and losses on investments supporting Health Care and Group Insurance liabilities and Large Case Pensions products (other than experience-rated and discontinued products) are reflected in our operating results. Realized capital gains and losses are determined on a specific identification basis. We reflect purchases and sales of debt and equity securities and alternative investments on the trade date. We reflect purchases and sales of mortgage loans and investment real estate on the closing date. Realized capital gains and losses on investments supporting Large Case Pensions’ experience-rated and discontinued products are not included in realized capital gains and losses in our statements of income and instead are credited directly to contract holders’ accounts, in the case of experience-rated products, or allocated to the reserve for anticipated future losses, in the case of discontinued products. The contract holders’ accounts are reflected in policyholders’ funds, and the reserve for anticipated future losses is reflected in future policy benefits on our balance sheets. Unrealized capital gains and losses on investments supporting Health Care and Group Insurance liabilities and Large Case Pensions products (other than experience-rated and discontinued products) are reflected in shareholders’ equity, net of tax, as a component of accumulated other comprehensive loss. Unrealized capital gains and losses on investments supporting Large Case Pensions’ experience-rated products are credited directly to contract holders’ accounts, which are reflected in policyholders’ funds on our balance sheets. Unrealized capital gains and losses on discontinued products are reflected in other long-term liabilities on our balance sheets. Refer to Note 19 for additional information on our discontinued products.
Premiums and Other Receivables	Premium Receivables Premium receivables include the uncollected amounts from fully-insured groups, individuals and government programs and are reported net of an allowance for estimated terminations and uncollectible accounts of $139 million and $146 million at December 31, 2016 and 2015, respectively. We estimate the allowance for estimated terminations and uncollectible accounts using management’s best estimate of collectability, taking into consideration the age of the outstanding amount, historical collection patterns and other economic factors. Other Receivables Other receivables include uncollected amounts from self-funded groups, pharmacy rebates, other government receivables, proceeds due from brokers on investment trades, provider advances and other miscellaneous amounts due to us. These receivables are reported net of an allowance for uncollectible accounts of $37 million and $20 million at December 31, 2016 and 2015, respectively. We estimate the allowance for uncollectible accounts using management’s best estimate of collectability, taking into consideration the age of the outstanding amount, historical collection patterns and other economic factors.
Reinsurance	Reinsurance Recoverables We utilize reinsurance agreements primarily to reduce our required capital and to facilitate the acquisition or disposition of certain insurance contracts. Ceded reinsurance agreements permit us to recover a portion of our losses from reinsurers, although they do not discharge our primary liability as the direct insurer of the risks reinsured. Failure of reinsurers to indemnify us could result in losses; however, we do not expect charges for unrecoverable reinsurance to have a material effect on our operating results or financial position. We evaluate the financial condition of our reinsurers and monitor concentrations of credit risk arising from similar geographic regions, activities or economic characteristics of our reinsurers. At December 31, 2016 , our reinsurance recoverables consisted primarily of amounts due from third parties that are rated consistent with companies that are considered to have the ability to meet their obligations.
Health Care Contract Acquisition Costs	Health Care Contract Acquisition Costs Health care benefits products included in our Health Care segment are cancelable by either the customer or the member monthly upon written notice. Acquisition costs related to our prepaid health care and health indemnity contracts are generally expensed as incurred. At December 31, 2016 and 2015 , the balance of our deferred acquisition costs was $412 million and $305 million , respectively, comprised primarily of commissions paid on our Medicare Supplement products. Deferred acquisition costs are recorded as other current assets or other long-term assets on our balance sheets and are amortized over the estimated life of the contracts.
Goodwill and Other Acquired Intangible Assets	Goodwill and Other Acquired Intangible Assets When we complete an acquisition, we apply the acquisition method of accounting, which requires the recognition of goodwill (the excess cost of the acquisition over the fair value of net assets acquired and identified intangible assets). We evaluate goodwill for impairment (at the reporting unit level) annually, or more frequently if circumstances indicate a possible impairment, by comparing an estimate of the fair value of the applicable reporting unit to its carrying value, including goodwill. If the carrying value exceeds fair value, we have historically compared the implied fair value of the applicable goodwill to its carrying amount to measure the amount of goodwill impairment, if any. Beginning in 2017, we adopted, on a prospective basis, the recently issued accounting standards update related to the methodology utilized to evaluate goodwill impairment. This update simplifies the methodology used to perform our annual, or interim, goodwill impairment evaluations. Our evaluation will be performed by comparing the estimated fair value of a reporting unit with its carrying amount. An impairment charge would be recognized when the carrying amount exceeds the estimated fair value of the reporting unit. Impairments, if any, would be classified as an operating expense. The fair value of each reporting unit substantially exceeded its carrying value in each of the years in the three-year period ended December 31, 2016 , and therefore there were no goodwill impairment losses recognized in any of those years. Our annual impairment tests were based on an evaluation of future discounted cash flows. These evaluations utilized the best information available to us at the time, including supportable assumptions and projections we believe are reasonable. Collectively, these evaluations were our best estimates of projected future cash flows. Our discounted cash flow evaluations used discount rates that correspond to a weighted-average cost of capital consistent with a market-participant view. The discount rates are consistent with those used for investment decisions and take into account the operating plans and strategies of the Health Care and Group Insurance segments. Certain other key assumptions utilized, including changes in membership, revenue, health care costs, operating expenses, impacts of health care reform fees, assessments and taxes, and effective tax rates, are based on estimates consistent with those utilized in our annual planning process that we believe are reasonable. If we do not achieve our earnings objectives, the assumptions and estimates underlying these goodwill impairment evaluations could be adversely affected, and we may impair a portion of our goodwill, which would adversely affect our operating results in the period of impairment. We report other acquired intangible assets at historical cost, net of accumulated amortization. Other acquired intangible assets primarily relate to provider networks, customer lists, value of business acquired (“VOBA”), technology and trademarks and are amortized over the useful-life based upon the pattern of future cash flows attributable to the asset. Other than VOBA and indefinite lived trademarks, other acquired intangible assets generally are amortized using the straight-line method. VOBA is amortized over the expected life of the acquired contracts in proportion to estimated premiums. Other intangible assets with indefinite lives are not amortized but are tested for impairment at least annually. We regularly evaluate whether events or changes in circumstances indicate that the carrying value of other acquired intangible assets may not be recoverable. If we determine that the carrying value of an asset may not be recoverable, we group the asset with other assets and liabilities at the lowest level for which independent identifiable cash flows are available and estimate the future undiscounted cash flows expected to result from future use of the asset group and its eventual disposition. If the sum of the expected undiscounted future cash flows is less than the carrying value of the asset group, we recognize an impairment loss for the amount by which the carrying value of the asset group exceeds its fair value. There were no material impairment losses on other acquired intangible assets recognized in any of the three years ended December 31, 2016 , 2015 or 2014 .
Property Plant And Equipment And Other Acquired Intangible Assets	Property and Equipment We report property and equipment at historical cost, net of accumulated depreciation. At December 31, 2016 and 2015 , the historical cost of property and equipment was each approximately $1.4 billion , and the related accumulated depreciation was $851 million and $774 million , respectively. We calculate depreciation primarily using the straight-line method over the estimated useful lives of the respective assets, which range from 10 to 40 years for buildings and 3 to 15 years for equipment. Depreciation expense was $125 million , $131 million and $137 million for the years ended December 31, 2016, 2015 and 2014, respectively. If we determine the carrying value of our property and equipment is not recoverable, an impairment charge is recorded. There were no material impairment losses on property and equipment recognized in any of the three years ended December 31, 2016, 2015 or 2014.
Separate Accounts	Separate Accounts Separate Accounts assets and liabilities in the Large Case Pensions segment represent funds maintained to meet specific objectives of contract holders who bear the investment risk. These assets and liabilities are carried at fair value. Net investment income and net realized capital gains and losses accrue directly to such contract holders. The assets of each account are legally segregated and are not subject to claims arising from our other businesses. Deposits, withdrawals, net investment income and net realized and net unrealized capital gains and losses on Separate Accounts assets are not reflected in our statements of income or cash flows. Management fees charged to contract holders are included in fees and other revenue and recognized over the period earned.
Health Care and Other Insurance Liabilities	Health Care Costs Payable Health care costs payable consist principally of unpaid fee-for-service medical, dental and pharmacy claims, capitation costs and other amounts due to health care providers pursuant to risk-sharing arrangements related to the Health Care segment’s Insured Commercial, Medicare and Medicaid products. Unpaid health care claims include our estimate of payments we will make on claims reported to us but not yet paid and for services rendered to members but not yet reported to us as of the balance sheet date (collectively, “IBNR”) in our Health Care segment. Also included in these estimates is the cost of services that will continue to be rendered after the balance sheet date if we are obligated to pay for such services in accordance with contractual or regulatory requirements. Such estimates are developed using actuarial principles and assumptions which consider, among other things, historical and projected claim submission and processing patterns, assumed and historical medical cost trends, historical utilization of medical services, claim inventory levels, changes in membership and product mix, seasonality and other relevant factors. We reflect changes in these estimates in health care costs in our operating results in the period they are determined. Capitation costs represent contractual monthly fees paid to participating physicians and other medical providers for providing medical care, regardless of the medical services provided to the member. Approximately 4% , 4% and 5% of our health care costs related to capitated arrangements in 2016, 2015 and 2014, respectively. Amounts due under risk-sharing arrangements are based on the terms of the underlying contracts with the providers and consider claims experience under the contracts through the balance sheet date. We develop our estimate of IBNR using actuarial principles and assumptions that consider numerous factors. Of those factors, we consider the analysis of historical and projected claim payment patterns (including claims submission and processing patterns) and the assumed health care cost trend rate (the year-over-year change in per member per month health care costs) to be the most critical assumptions. In developing our estimate of IBNR, we consistently apply these actuarial principles and assumptions each period, with consideration to the variability of related factors. There have been no significant changes to the methodologies or assumptions used to calculate IBNR in 2016. We analyze historical claim payment patterns by comparing claim incurred dates (i.e., the date services were provided) to claim payment dates to estimate “completion factors.” We estimate completion factors by aggregating claim data based on the month of service and month of claim payment and estimating the percentage of claims incurred for a given month that are complete by each month thereafter. For any given month, substantially all claims are paid within six months of the date of service, but it can take up to 48 months or longer before all of the claims are completely resolved and paid. These historically-derived completion factors are then applied to claims paid through the financial statement date to estimate the ultimate claim cost for a given month’s incurred claim activity. The difference between the estimated ultimate claim cost and the claims paid through the financial statement date represents our estimate of claims remaining to be paid as of the financial statement date and is included in our health care costs payable. We use completion factors predominantly to estimate reserves for claims with claim incurred dates greater than three months prior to the financial statement date. The completion factors we use reflect judgments and possible adjustments based on data such as claim inventory levels, claim submission and processing patterns and, to a lesser extent, other factors such as changes in health care cost trend rates, changes in membership and changes in product mix. If claims are submitted or processed on a faster (slower) pace than prior periods, the actual claims may be more (less) complete than originally estimated using our completion factors, which may result in reserves that are higher (lower) than the ultimate cost of claims. Because claims incurred within three months prior to the financial statement date are less mature, we use a combination of historically-derived completion factors and the assumed health care cost trend rate to estimate the ultimate cost of claims incurred for these months. We place a greater emphasis on the assumed health care cost trend rate for the most recent claim incurred dates as these months may be influenced by seasonal patterns and changes in membership and product mix. Our health care cost trend rate is affected by changes in per member utilization of medical services as well as changes in the unit cost of such services. Many factors influence the health care cost trend rate, including our ability to manage health care costs through product design, negotiation of favorable provider contracts and medical management programs, as well as the mix of our business. The health status of our members, aging of the population and other demographic characteristics, advances in medical technology and other factors continue to contribute to rising per member utilization and unit costs. Changes in health care practices, inflation, new technologies, increases in the cost of prescription drugs (including specialty pharmacy drugs), direct-to-consumer marketing by pharmaceutical companies, clusters of high-cost cases, claim intensity, changes in the regulatory environment, health care provider or member fraud and numerous other factors also contribute to the cost of health care and our health care cost trend rate. For each reporting period, we use an extensive degree of judgment in the process of estimating our health care costs payable. As a result, considerable variability and uncertainty is inherent in such estimates; and the adequacy of such estimates is highly sensitive to changes in assumed completion factors and the assumed health care cost trend rates. For each reporting period we recognize the actuarial best estimate of health care costs payable considering the potential volatility in assumed completion factors and health care cost trend rates, as well as other factors. We believe our estimate of health care costs payable is reasonable and adequate to cover our obligations at December 31, 2016; however, actual claim payments may differ from our estimates. A worsening (or improvement) of our health care cost trend rates or changes in completion factors from those that we assumed in estimating health care costs payable at December 31, 2016 would cause these estimates to change in the near term, and such a change could be material. Each quarter, we re-examine previously established health care costs payable estimates based on actual claim payments for prior periods and other changes in facts and circumstances. Given the extensive degree of judgment in this estimate, it is possible that our estimates of health care costs payable could develop either favorably (that is, our actual health care costs for the period were less than we estimated) or unfavorably. The changes in our estimate of health care costs payable may relate to a prior quarter, prior year or earlier periods. For our roll forward of our health care costs payable, refer to Note 7 . Our reserving practice is to consistently recognize the actuarial best estimate of our ultimate liability for health care costs payable. Unpaid claims Unpaid claims consist primarily of reserves associated with certain short-duration group disability and term life insurance contracts in the Group Insurance segment, including an estimate for IBNR in our Group Insurance segment as of the balance sheet date. Reserves associated with certain short-duration group disability and term life insurance contracts are based upon our estimate of the present value of future benefits, which is based on assumed investment yields and assumptions regarding mortality, morbidity and recoveries from the U.S. Social Security Administration. We develop our estimate of IBNR using actuarial principles and assumptions which consider, among other things, contractual requirements, claim incidence rates, claim recovery rates, seasonality and other relevant factors. We discount certain claim liabilities related to group long-term disability and life insurance waiver of premium contracts. The discount rates generally reflect our expected investment returns for the investments supporting all incurral years of these liabilities. The discount rates for retrospectively-rated contracts are set at contractually specified levels. Our estimates of unpaid claims are subject to change due to changes in the underlying experience of the insurance contracts, changes in investment yields or other factors, and these changes are recorded in current and future benefits in our statements of income in the period they are determined. Refer to Note 7 for additional information related to our long-term disability unpaid claim liabilities. We estimate our reserve for claims IBNR for life products largely based on completion factors. The completion factors we use are based on our historical experience and reflect judgments and possible adjustments based on data such as claim inventory levels, claim payment patterns, changes in business volume and other factors. If claims are submitted or processed on a faster (slower) pace than historical periods, the actual claims may be more (less) complete than originally estimated using our completion factors, which may result in reserves that are higher (lower) than required to cover future life benefit payments. At December 31, 2016, we held $246 million in reserves for life claims incurred but not yet reported to us. There have been no significant changes to the methodologies or assumptions used to calculate IBNR in 2016. Future policy benefits Future policy benefits consist primarily of reserves for limited payment pension and annuity contracts in the Large Case Pensions segment and long-duration group life and long-term care insurance contracts in the Group Insurance segment. Reserves for limited payment contracts are computed using actuarial principles that consider, among other things, assumptions reflecting anticipated mortality, retirement, expense and interest rate experience. Such assumptions generally vary by plan, year of issue and policy duration. Assumed interest rates on such contracts ranged from .8% to 11.3% in both 2016 and 2015 . We periodically review mortality assumptions against both industry standards and our experience. Reserves for long-duration group life and long-term care contracts represent our estimate of the present value of future benefits to be paid to or on behalf of policyholders less the present value of future net premiums. Assumed interest rates on such contracts ranged from 2.5% to 8.8% in both 2016 and 2015 . Our estimate of the present value of future benefits under such contracts is based upon mortality, morbidity and interest rate assumptions. Policyholders’ funds Policyholders’ funds consist primarily of reserves for pension and annuity investment contracts in the Large Case Pensions segment and customer funds associated with group life and health contracts in the Health Care and Group Insurance segments. Reserves for such contracts are equal to cumulative deposits less withdrawals and charges plus credited interest thereon, net of experience-rated adjustments. In 2016 , interest rates for pension and annuity investment contracts ranged from 3.5% to 15.9% , and interest rates for group life and health contracts ranged from 0% to 2.4% . In 2015 , interest rates for pension and annuity investment contracts ranged from 3.5% to 14.7% , and interest rates for group life and health contracts ranged from 0% to 2.7% . Reserves for contracts subject to experience rating reflect our rights as well as the rights of policyholders and plan participants. We also hold funds for health savings accounts (“HSAs”) on behalf of members associated with high deductible health plans. These amounts are held to pay for qualified health care expenses incurred by these members. The HSA balances were approximately $1.7 billion and $1.5 billion at December 31, 2016 and 2015 , respectively, and are reflected in other current assets with a corresponding liability in policyholder funds. We review health care and other insurance liabilities periodically. We reflect any necessary adjustments during the current period in operating results. While the ultimate amount of claims and related expenses are dependent on future developments, it is management’s opinion that the liabilities that have been established are adequate to cover such costs. The health care and other insurance liabilities that are expected to be paid within twelve months are classified as current on our balance sheets. Premium Deficiency Reserves We evaluate our insurance contracts to determine if it is probable that a loss will be incurred. We recognize a premium deficiency loss when it is probable that expected future claims, including maintenance costs (for example, direct costs such as claim processing costs), will exceed existing reserves plus anticipated future premiums and reinsurance recoveries. Anticipated investment income is considered in the calculation of premium deficiency losses for short-duration contracts. For purposes of determining premium deficiency losses, contracts are grouped consistent with our method of acquiring, servicing and measuring the profitability of such contracts. In the second and third quarters of 2016, we recorded premium deficiency reserves totaling $85 million related to anticipated future losses for the 2016 coverage year in our individual Commercial products. We did not have any premium deficiency reserves at December 31, 2016 or 2015 .
Revenue Recognition	Revenue Recognition Premium Revenue Health care premiums are recognized as income in the month in which the enrollee is entitled to receive health care services. Health care premiums are reported net of an allowance for estimated terminations and uncollectible amounts. Additionally, premium revenue subject to the ACA’s minimum Medical Loss Ratio (“MLR”) rebate requirements is recorded net of the estimated minimum MLR rebates for the current calendar year. Other premium revenue for group life, long-term care and disability products is recognized as income, net of allowances for termination and uncollectible accounts, over the term of the coverage. Other premium revenue for Large Case Pensions’ limited payment pension and annuity contracts is recognized as revenue in the period received. Premiums related to unexpired contractual coverage periods are reported as unearned premiums in our balance sheets and recognized as revenue when earned. Some of our contracts allow for premiums to be adjusted to reflect actual experience or the relative health status of members. Such adjustments are reasonably estimable at the outset of the contract, and adjustments to those estimates are made based on actual experience of the customer emerging under the contract and the terms of the underlying contract. Administrative Service Contract (“ASC”) Fees Fees and other revenue consists primarily of ASC fees which are received in exchange for performing certain claim processing and member services for health and disability members and are recognized as revenue over the period the service is provided. Fees and other revenue also includes fees related to our pharmacy benefit management and workers’ compensation administrative services products and services. Some of our contracts include guarantees with respect to certain functions, such as customer service response time, claim processing accuracy and claim processing turnaround time, as well as certain guarantees that a plan sponsor’s benefit claim experience will fall within a certain range. With any of these guarantees, we are financially at risk if the conditions of the arrangements are not met, although the maximum amount at risk is typically limited to a percentage of the fees otherwise payable to us by the customer involved. Each period we estimate our obligations under the terms of these guarantees and record it as an offset to our ASC fees. In addition, fees and other revenue also include charges assessed against contract holders’ funds for contract fees, participant fees and asset charges related to pension and annuity products in the Large Case Pensions segment. Other amounts received on pension and annuity investment-type contracts are reflected as deposits and are not recorded as revenue. Some of our Large Case Pensions contract holders have the contractual right to purchase annuities with life contingencies using the funds they maintain on deposit with us. Since these products are considered an insurance contract, when the contract holder makes this election, we treat the accumulated investment balance as a single premium and reflect it as both premiums and current and future benefits in our statements of income. Accounting for the Medicare Part D Prescription Drug Program Plans (“PDPs”) We were selected by the Centers for Medicare & Medicaid Services (“CMS”) to be a national provider of PDPs in all 50 states to both individuals and employer groups in 2016 , 2015 and 2014 . Under these annual contracts, CMS pays us a portion of the premium, a portion of, or a capitated fee for, catastrophic drug costs and a portion of the health care costs for low-income Medicare beneficiaries and provides a risk-sharing arrangement to limit our exposure to unexpected expenses. We recognize premiums received from, or on behalf of, members or CMS and capitated fees as premium revenue ratably over the contract period. We expense the cost of covered prescription drugs as incurred. Costs associated with low-income Medicare beneficiaries (deductible, coinsurance, etc.) and the catastrophic drug costs paid in advance by CMS are recorded as a liability and offset health care costs when incurred. For individual PDP coverage, the risk-sharing arrangement provides a risk corridor whereby the amount we received in premiums from members and CMS based on our annual bid is compared to our actual drug costs incurred during the contract year. Based on the risk corridor provision and PDP activity-to-date, we record an estimated risk-sharing receivable or payable on a quarterly basis as an adjustment to premium revenue. We perform a reconciliation of the final risk-sharing, low-income subsidy and catastrophic amounts after the end of each contract year. Health Care Reform Health Insurer Fee Since January 1, 2014, the ACA imposes an annual premium-based health insurer fee (“HIF”) for each calendar year payable in September which is not deductible for tax purposes. We are required to estimate a liability for the HIF at the beginning of the calendar year in which the fee is payable with a corresponding deferred asset that is amortized ratably to general and administrative expense over the calendar year. We record the liability for the health insurer fee in accrued expenses and other current liabilities and record the deferred asset in other current assets in our consolidated financial statements. In 2016, 2015 and 2014, general and administrative expense includes $837 million , $857 million and $605 million , respectively, related to our share of the HIF. In December 2015, the Consolidated Appropriation Act was enacted which included a one year suspension in 2017 of the HIF. Public Exchanges We are participating in certain public health insurance exchanges established pursuant to the ACA (“Public Exchanges”). Under regulations established by the U.S. Department of Health and Human Services (“HHS”), HHS pays us a portion of the premium (“Premium Subsidy”) and a portion of the health care costs (“Cost Sharing Subsidy”) for low-income individual Public Exchange members. In addition, HHS administers the ACA’s Reinsurance, Risk Adjustment and Risk Corridor (the “3Rs”) risk management programs. We recognize monthly premiums received from Public Exchange members and the Premium Subsidy as premium revenue ratably over the contract period. The Cost Sharing Subsidy offsets health care costs based on our estimate of the portion of claim costs incurred by our low income individual Public Exchange members that qualify for reimbursement by HHS. We record a liability or a receivable depending on whether qualifying health care costs incurred are less than or greater than the Cost Sharing Subsidy received to date. Reinsurance The ACA established a temporary reinsurance program that expired at the end of 2016. Under this program, all issuers of major medical commercial insurance products and self-insured plan sponsors are required to contribute funding in amounts set by HHS. Funds collected will be utilized to reimburse issuers’ high claims costs incurred for qualified individual members. The expense related to this required funding is reflected in general and administrative expenses for all of our insurance products with the exception of products associated with qualified individual members; this expense for qualified individual members is reflected as a reduction of premium revenue. In 2016, 2015 and 2014, our estimated contribution to the funding of the ACA’s reinsurance program was $118 million , $210 million and $336 million , respectively, which was recorded in general and administrative expenses. When annual claim costs incurred by our qualified individual members exceed a specified attachment point, we are entitled to certain reimbursements from this program. We record a receivable and offset health care costs to reflect our estimate of these recoveries. Risk Adjustment The ACA established a permanent risk adjustment program to transfer funds from qualified individual and small group insurance plans with below average risk scores to plans with above average risk scores. Based on the risk of our qualified plan members relative to the average risk of members of other qualified plans in comparable markets, we estimate our ultimate risk adjustment receivable or payable for the current calendar year and reflect the pro-rata year-to-date impact as an adjustment to our premium revenue. Risk Corridor The ACA established a temporary risk sharing program, which expired at the end of 2016, for qualified individual and small group insurance plans. Under this program we make (or receive) a payment to (or from) HHS based on the ratio of allowable costs to target costs (as defined by the ACA). We record a risk corridor receivable or payable as an adjustment to premium revenue on a pro-rata year-to-date basis based on our estimate of the ultimate risk sharing amount for the current calendar year. At December 31, 2016, we did not record any ACA risk corridor receivables related to the 2016 or 2015 program years or any amount in excess of HHS’s announced pro-rated funding amount for the 2014 program year because payments from HHS are uncertain. We expect to perform an annual final reconciliation and settlement with HHS of the Cost Sharing Subsidy and 3Rs in each subsequent year, except for the final reconciliation and settlement of the 2014 Cost Sharing Subsidy which occurred in 2016. Refer to Note 8 for additional information related to the 3Rs.
Selling, General and Administrative Expenses, Policy [Policy Text Block]	Voluntary Early Retirement Program In September 2016, we announced a voluntary early retirement program (the “Program”). Under the terms of the Program, eligible employees elected early retirement during the fourth quarter of 2016. We recorded a liability associated with the Program in accrued expenses and other current liabilities and an expense in general and administrative expenses of $330 million pretax at and for the year ended December 31, 2016, respectively. Selling Expenses Selling expenses include broker commissions, the variable component of our internal sales force compensation and premium taxes.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	Stock-Based Compensation We record compensation expense for stock-based awards over their vesting periods primarily based on the estimated fair value at the grant date. For stock appreciation rights (“SARs”), the fair value is estimated using the Black-Scholes option-pricing model. For restricted stock units (“RSUs”) and performance stock units (“PSUs”), the fair value is equal to the market price of the Company's common stock on the date of grant. For market stock units (“MSUs”) and performance stock appreciation rights (“PSARs”), the fair value is estimated using Monte Carlo simulations. Refer to Note 12 for additional information related to our stock-based employee incentive plans.
Income Taxes	Income Taxes We are taxed at the statutory corporate income tax rates after adjusting income reported for financial statement purposes for certain items. We recognize deferred income tax assets and liabilities for the differences between the financial and income tax reporting basis of assets and liabilities based on enacted tax rates and laws. Valuation allowances are provided when it is considered more likely than not that deferred tax assets will not be realized. Deferred income tax expense or benefit primarily reflects the net change in deferred income tax assets and liabilities during the year. Our current income tax provision reflects the tax results of revenues and expenses currently taxable or deductible. Penalties and interest on our tax positions are classified as a component of our income tax provision.
Pension and Other Postretirement Plans, Policy [Policy Text Block]	Measurement of Defined Benefit Pension and Other Postretirement Employee Benefit (“OPEB”) Plans We sponsor defined benefit pension plans (“pension plans”) and OPEB plans for our employees and retirees. We recognize the funded status of our pension plans and OPEB plans on the consolidated balance sheets based on our year-end measurements of plan assets and benefit obligations. Prepaid pension and OPEB benefits represent prepaid costs related to our pension plans and are reported with other current and long-term assets. Liabilities associated with pension plans and OPEB plans are reported within current and other long-term liabilities based on the amount by which the actuarial present value of benefits payable in the next twelve months included in the benefit obligation exceeds the fair value of plan assets.
Earnings Per Share, Policy [Policy Text Block]	Earnings Per Share We calculate basic earnings per share based on the weighted average number of common shares outstanding for the period. Diluted earnings per common share is calculated based on the weighted average number of common shares outstanding plus the dilutive effect of outstanding SARs, MSUs, PSUs, RSUs and PSARs using the treasury stock method. Refer to Notes 12 and 15 for additional information.
New Accounting Standards	New Accounting Standards Amendments to the Consolidation Analysis Effective January 1, 2016, we adopted new accounting guidance related to the evaluation of consolidation for certain legal entities. The new guidance changes how a reporting entity assesses consolidation, including whether an entity is considered a variable interest entity, determination of the primary beneficiary and how related parties are considered in the analysis. The adoption of this new guidance required more of our other investments to be considered variable interest entities; however, it did not require additional investments to be consolidated or de-consolidated or have a material impact on our financial position or operating results. Our variable interest entity disclosures as of December 31, 2015 were retrospectively adjusted to conform with the new accounting guidance. Refer to Note 4 for further discussion. Simplifying the Presentation of Debt Issuance Costs Effective January 1, 2016, we adopted new accounting guidance related to the financial statement presentation of all debt issuance costs, including those related to line-of-credit arrangements. The new guidance requires debt issuance costs to be presented as a direct deduction from the carrying amount of our debt liability, consistent with the approach used for debt premiums or discounts. We also elected to report debt issuance costs associated with any line-of-credit arrangements as a direct deduction from the carrying amount of our debt liability. Amortization of debt issuance costs also will be reported in our statements of income in interest expense, as opposed to general and administrative expenses. We are applying this new guidance on a full retrospective basis, with all prior periods restated for the new presentation. As a result of adopting this guidance, we reclassified $43 million of other current and long-term assets as a reduction of long-term debt on our balance sheet at December 31, 2015. Additionally, we reclassified an immaterial amount of general and administrative expenses into interest expense for the year ended December 31, 2015. Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent) Effective January 1, 2016, we adopted new accounting guidance related to the presentation of investments in certain entities that calculate net asset value per share (or its equivalent). The new guidance removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the net asset value per share practical expedient. This new guidance is applicable to certain of our investments that reside in our general accounts, separate accounts and employee benefit plans. The adoption of this new guidance did not have a material impact on our financial position or operating results. Improvements to Employee Share-Based Payment Accounting Effective April 1, 2016, we elected to early adopt new accounting guidance related to the accounting for and financial statement presentation of employee share-based payments. As a result of adopting this new guidance, we recognized $29 million of excess tax benefits in our statements of income that previously would have been recorded in additional paid-in capital for the year ended December 31, 2016, and correspondingly reclassified the excess tax benefits for the year ended December 31, 2016 from financing activities to operating activities in our statements of cash flows. We applied each of these provisions on a prospective basis, with adjustments reflected as of January 1, 2016, and prior periods were not retrospectively adjusted. Our ability under the new guidance to withhold more shares to satisfy our statutory income tax obligations had no impact on our financial statements and was adopted on a modified retrospective basis. We continue to estimate expected forfeitures of share-based payment awards in each period. Disclosures about Short-Duration Insurance Contracts Effective December 31, 2016, we adopted new accounting guidance related to the disclosure of short-duration insurance contracts. The new guidance requires insurance companies that issue short-duration contracts to include additional disclosures about those insurance liabilities, including disaggregation of certain disclosures, as appropriate. The adoption of this new guidance did not have an impact on our financial position or operating results; however, the new guidance required additional disclosure for our health care cost payable and unpaid claims short-duration insurance liabilities that reside in our Health Care and Group Insurance segments.

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Total investments	Total investments at December 31, 2016 and 2015 were as follows: 2016 2015 (Millions) Current Long-term Total Current Long-term Total Debt and equity securities available for sale $ 2,876 $ 18,866 $ 21,742 $ 2,877 $ 18,446 $ 21,323 Mortgage loans 170 1,341 1,511 127 1,427 1,554 Other investments — 1,626 1,626 11 1,792 1,803 Total investments $ 3,046 $ 21,833 $ 24,879 $ 3,015 $ 21,665 $ 24,680
Debt and Equity Available-for-sale Securities	Debt and equity securities available for sale at December 31, 2016 and 2015 were as follows: (Millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value December 31, 2016 Debt securities: U.S. government securities $ 1,643 $ 51 $ — $ 1,694 States, municipalities and political subdivisions 5,047 152 (61 ) 5,138 U.S. corporate securities 8,145 385 (55 ) 8,475 Foreign securities 2,958 163 (33 ) 3,088 Residential mortgage-backed securities 793 11 (9 ) 795 Commercial mortgage-backed securities 1,382 5 (39 ) (1) 1,348 Other asset-backed securities 1,077 7 (9 ) (1) 1,075 Redeemable preferred securities 22 5 — 27 Total debt securities 21,067 779 (206 ) 21,640 Equity securities 84 20 (2 ) 102 Total debt and equity securities (2) $ 21,151 $ 799 $ (208 ) $ 21,742 December 31, 2015 Debt securities: U.S. government securities $ 1,804 $ 69 $ (1 ) $ 1,872 States, municipalities and political subdivisions 4,890 244 (9 ) 5,125 U.S. corporate securities 7,982 340 (147 ) 8,175 Foreign securities 2,910 148 (61 ) 2,997 Residential mortgage-backed securities 914 17 (6 ) 925 Commercial mortgage-backed securities 1,262 17 (9 ) (1) 1,270 Other asset-backed securities 910 3 (19 ) (1) 894 Redeemable preferred securities 33 11 — 44 Total debt securities 20,705 849 (252 ) 21,302 Equity securities 23 4 (6 ) 21 Total debt and equity securities (2) $ 20,728 $ 853 $ (258 ) $ 21,323 (1) At both December 31, 2016 and 2015 , we held securities for which we previously recognized an immaterial amount of non-credit related impairments in accumulated other comprehensive loss. These securities each had an immaterial amount of net unrealized capital gains at December 31, 2016 and 2015 , respectively. (2) Investment risks associated with our experience-rated and discontinued products generally do not impact our operating results (refer to Note 19 for additional information on our accounting for discontinued products). At December 31, 2016 , debt and equity securities with a fair value of approximately $2.9 billion , gross unrealized capital gains of $195 million and gross unrealized capital losses of $35 million and, at December 31, 2015 , debt and equity securities with a fair value of approximately $3.0 billion , gross unrealized capital gains of $209 million and gross unrealized capital losses of $68 million were included in total debt and equity securities, but support our experience-rated and discontinued products. Changes in net unrealized capital gains (losses) on these securities are not reflected in accumulated other comprehensive income.
Fair value of debt securities by contractual maturity	The fair value of debt securities at December 31, 2016 is shown below by contractual maturity. Actual maturities may differ from contractual maturities because securities may be restructured, called or prepaid, or we intend to sell a security prior to maturity. (Millions) Amortized Cost Fair Value Due to mature: Less than one year $ 1,380 $ 1,394 One year through five years 6,604 6,758 After five years through ten years 5,059 5,162 Greater than ten years 4,772 5,108 Residential mortgage-backed securities 793 795 Commercial mortgage-backed securities 1,382 1,348 Other asset-backed securities 1,077 1,075 Total $ 21,067 $ 21,640
Debt and Equity Securities in an Unrealized Capital Loss Position	Summarized below are the debt and equity securities we held at December 31, 2016 and 2015 that were in an unrealized capital loss position, aggregated by the length of time the investments have been in that position: Less than 12 months Greater than 12 months Total (1) (Millions, except number of securities) Number of Securities Fair Value Unrealized Losses Number of Securities Fair Value Unrealized Losses Number of Securities Fair Value Unrealized Losses December 31, 2016 Debt securities: U.S. government securities 26 $ 39 $ — 1 $ 1 $ — 27 $ 40 $ — States, municipalities and political subdivisions 865 2,228 58 37 75 3 902 2,303 61 U.S. corporate securities 1,428 2,277 44 114 101 11 1,542 2,378 55 Foreign securities 649 970 27 62 76 6 711 1,046 33 Residential mortgage-backed securities 188 455 8 104 17 1 292 472 9 Commercial mortgage-backed securities 285 1,038 39 3 3 — 288 1,041 39 Other asset-backed securities 226 403 4 208 177 5 434 580 9 Total debt securities 3,667 7,410 180 529 450 26 4,196 7,860 206 Equity securities 2 3 — 8 3 2 10 6 2 Total debt and equity securities (1) 3,669 $ 7,413 $ 180 537 $ 453 $ 28 4,206 $ 7,866 $ 208 December 31, 2015 Debt securities: U.S. government securities 48 $ 67 $ — 6 $ 13 $ — 54 $ 80 $ — States, municipalities and political subdivisions 286 714 6 42 92 3 328 806 9 U.S. corporate securities 2,751 3,169 131 215 144 16 2,966 3,313 147 Foreign securities 793 1,102 50 82 89 11 875 1,191 61 Residential mortgage-backed securities 212 329 3 177 89 3 389 418 6 Commercial mortgage-backed securities 226 562 9 30 24 — 256 586 9 Other asset-backed securities 626 653 16 69 67 4 695 720 20 Total debt securities 4,942 6,596 215 621 518 37 5,563 7,114 252 Equity securities 11 — 5 5 2 1 16 2 6 Total debt and equity securities (1) 4,953 $ 6,596 $ 220 626 $ 520 $ 38 5,579 $ 7,116 $ 258 (1) At December 31, 2016 and 2015 , debt and equity securities in an unrealized capital loss position of $35 million and $68 million , respectively, and with related fair value of $890 million and $966 million , respectively, related to experience-rated and discontinued products.
Maturity dates for debt securities	The maturity dates for debt securities in an unrealized capital loss position at December 31, 2016 were as follows: Supporting discontinued and experience-rated products Supporting remaining products Total (Millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Due to mature: Less than one year $ 5 $ — $ 201 $ — $ 206 $ — One year through five years 70 1 2,083 28 2,153 29 After five years through ten years 288 9 1,559 43 1,847 52 Greater than ten years 317 17 1,244 51 1,561 68 Residential mortgage-backed securities 16 1 456 8 472 9 Commercial mortgage-backed securities 174 6 867 33 1,041 39 Other asset-backed securities 20 1 560 8 580 9 Total $ 890 $ 35 $ 6,970 $ 171 $ 7,860 $ 206
Activity in mortgage loan portfolio	During 2016 and 2015 we had the following activity in our mortgage loan portfolio: (Millions) 2016 2015 New mortgage loans $ 190 $ 213 Mortgage loans fully-repaid 173 163 Mortgage loans foreclosed 8 9
Mortgage loan internal credit rating	Based upon our most recent assessments at December 31, 2016 and 2015 , our mortgage loans were given the following credit quality indicators: (In Millions, except credit ratings indicator) 2016 2015 1 $ 45 $ 66 2 to 4 1,449 1,467 5 and 6 17 21 7 — — Total $ 1,511 $ 1,554
Future Mortgage Loan Payments	At December 31, 2016 scheduled mortgage loan principal repayments were as follows: (Millions) 2017 $ 171 2018 216 2019 123 2020 166 2021 253 Thereafter 582
Sources of net investment income	Sources of net investment income for 2016 , 2015 and 2014 were as follows: (Millions) 2016 2015 2014 Debt securities $ 772 $ 794 $ 801 Mortgage loans 95 91 108 Other investments 82 78 76 Gross investment income 949 963 985 Investment expenses (39 ) (46 ) (39 ) Net investment income (1) $ 910 $ 917 $ 946 (1) Net investment income includes $208 million , $248 million and $289 million for 2016 , 2015 and 2014 , respectively, related to investments supporting our experience-rated and discontinued products.
Net realized capital gains (losses)	Net realized capital (losses) gains for the three years ended December 31, 2016 , 2015 and 2014 , excluding amounts related to experience-rated contract holders and discontinued products, were as follows: (Millions) 2016 2015 2014 Other-than-temporary impairment (“OTTI”) losses on debt securities recognized in earnings $ (30 ) $ (64 ) $ (5 ) Other net realized capital gains (losses) 116 (1 ) 85 Net realized capital gains (losses) $ 86 $ (65 ) $ 80
Proceeds and related gross realized capital gains and losses from the sale of debt securities	Excluding amounts related to experience-rated and discontinued products, proceeds from the sale of available for sale debt and equity securities and the related gross realized capital gains and losses for 2016 , 2015 and 2014 were as follows (1) : (Millions) 2016 2015 2014 Proceeds on sales $ 6,725 $ 4,987 $ 4,615 Gross realized capital gains 155 83 109 Gross realized capital losses 61 76 36 (1) The proceeds on sales and gross realized capital gains and losses exclude the impact of the sales of short-term debt securities which primarily relate to our investments in mutual funds. These investments were excluded from the disclosed amounts because they represent an immaterial amount of aggregate gross realized capital gains or losses and have a high volume of sales activity.
Variable Interest Entity Assets Included on the Balance Sheet [Member]
Schedule of Variable Interest Entities [Table Text Block]	The total amount of other variable interest holder VIE assets included in long term investments on our balance sheets at December 31, 2016 and 2015 were as follows: (Millions) December 31, December 31, 2015 Hedge fund investments $ 384 $ 418 Private equity investments 454 443 Real estate partnerships 278 254 Total $ 1,116 $ 1,115
Variable Interest Entity Assets and Liabilities [Member]
Schedule of Variable Interest Entities [Table Text Block]	The carrying value of the total assets and liabilities of our other variable interest holder VIE investments at December 31, 2016 and 2015 were as follows: (Millions) December 31, December 31, 2015 Assets: Hedge fund investments $ 32,926 $ 33,066 Private equity investments 25,368 28,552 Real estate partnerships 6,743 6,809 Total $ 65,037 $ 68,427 Liabilities: Hedge fund investments $ 2,819 $ 3,535 Private equity investments 2,354 3,236 Real estate partnerships 4,938 5,045 Total $ 10,111 $ 11,816

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Financial Instruments [Abstract]
Fair Value of Financial Assets	Financial assets and liabilities measured at fair value on a recurring basis in our balance sheets at December 31, 2016 and 2015 were as follows: (Millions) Level 1 Level 2 Level 3 Total December 31, 2016 Assets: Debt securities: U.S. government securities $ 1,514 $ 180 $ — $ 1,694 States, municipalities and political subdivisions — 5,137 1 5,138 U.S. corporate securities — 8,395 80 8,475 Foreign securities — 3,067 21 3,088 Residential mortgage-backed securities — 795 — 795 Commercial mortgage-backed securities — 1,348 — 1,348 Other asset-backed securities — 1,075 — 1,075 Redeemable preferred securities — 26 1 27 Total debt securities 1,514 20,023 103 21,640 Equity securities 59 — 43 102 Derivatives — — — — Total $ 1,573 $ 20,023 $ 146 $ 21,742 Liabilities: Derivatives $ — $ — $ — $ — December 31, 2015 Assets: Debt securities: U.S. government securities $ 1,671 $ 201 $ — $ 1,872 States, municipalities and political subdivisions — 5,124 1 5,125 U.S. corporate securities — 8,111 64 8,175 Foreign securities — 2,972 25 2,997 Residential mortgage-backed securities — 925 — 925 Commercial mortgage-backed securities — 1,270 — 1,270 Other asset-backed securities — 894 — 894 Redeemable preferred securities — 39 5 44 Total debt securities 1,671 19,536 95 21,302 Equity securities 2 — 19 21 Derivatives — 20 — 20 Total $ 1,673 $ 19,556 $ 114 $ 21,343 Liabilities: Derivatives $ — $ 88 $ — $ 88
Changes in the Balances of Level 3 Financial Assets	The changes in the balances of Level 3 financial assets during 2016 were as follows: (Millions) Foreign securities U.S. corporate securities Equity securities Other Total Beginning balance $ 25 $ 64 $ 19 $ 6 $ 114 Net realized and unrealized capital (losses) gains: Included in earnings — (15 ) — — (15 ) Included in other comprehensive income — (4 ) 11 (3 ) 4 Other (1) — — 3 — 3 Purchases 16 41 10 33 100 Sales (8 ) (3 ) — (5 ) (16 ) Settlements (2 ) (3 ) — — (5 ) Transfers out of Level 3, net (10 ) — — (29 ) (39 ) Ending balance $ 21 $ 80 $ 43 $ 2 $ 146 (1) Reflects realized and unrealized capital gains and losses on investments supporting our experience-rated and discontinued products, which do not impact our operating results. The changes in the balances of Level 3 financial assets during 2015 were as follows: (Millions) Foreign securities U.S. corporate securities Equity securities Other Total Beginning balance $ 32 $ 58 $ 18 $ 54 $ 162 Net realized and unrealized capital gains (losses): Included in earnings — (6 ) — — (6 ) Included in other comprehensive income — 2 2 — 4 Other (1) (1 ) — (3 ) — (4 ) Purchases — 11 2 24 37 Sales (5 ) (1 ) — — (6 ) Settlements (1 ) — — (9 ) (10 ) Transfers out of Level 3, net — — — (63 ) (63 ) Ending balance $ 25 $ 64 $ 19 $ 6 $ 114 (1) Reflects realized and unrealized capital gains and losses on investments supporting our experience-rated and discontinued products, which do not impact our operating results.
Gross Transfers into (out of) Level 3	The total gross transfers into (out of) Level 3 during the years ended December 31, 2016 and 2015 were as follows: (Millions) 2016 2015 Gross transfers into Level 3 $ — $ 1 Gross transfers out of Level 3 (39 ) (64 ) Net transfers out of Level 3 $ (39 ) $ (63 )
Carrying Value and Estimated Fair Value of Certain Financial Instruments	The carrying value and estimated fair value classified by level of fair value hierarchy for our financial instruments carried on our balance sheets at adjusted cost or contract value at December 31, 2016 and 2015 were as follows: Carrying Value Estimated Fair Value (Millions) Level 1 Level 2 Level 3 Total December 31, 2016 Assets: Mortgage loans $ 1,511 $ — $ — $ 1,540 $ 1,540 Bank loans 8 — — 8 8 Equity securities (1) 35 N/A N/A N/A N/A Liabilities: Investment contract liabilities: With a fixed maturity 8 — — 8 8 Without a fixed maturity 378 — — 364 364 Long-term debt 20,661 — 21,468 — 21,468 Carrying Value Estimated Fair Value (Millions) Level 1 Level 2 Level 3 Total December 31, 2015 Assets: Mortgage loans $ 1,554 $ — $ — $ 1,599 $ 1,599 Bank loans 193 — 180 8 188 Equity securities (1) 35 N/A N/A N/A N/A Liabilities: Investment contract liabilities: With a fixed maturity 9 — — 9 9 Without a fixed maturity 371 — — 351 351 Long-term debt 7,785 — 8,227 — 8,227 (1) It was not practical to estimate the fair value of these cost-method investments as it represents shares of unlisted companies.
Separate Account Financial Assets	Separate Accounts financial assets at December 31, 2016 and 2015 were as follows: 2016 2015 (Millions) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Debt securities $ 766 $ 2,378 $ — $ 3,144 $ 751 $ 2,382 $ 4 $ 3,137 Equity securities 166 6 — 172 170 5 — 175 Common/collective trusts — 582 — 582 — 540 — 540 Total (1) $ 932 $ 2,966 $ — $ 3,898 $ 921 $ 2,927 $ 4 $ 3,852 (1) Excludes $93 million and $183 million of cash and cash equivalents and other receivables at December 31, 2016 and 2015 , respectively.
Offsetting Assets	Financial assets, including derivative assets, subject to offsetting and enforceable master netting arrangements as of December 31, 2016 and December 31, 2015 were as follows: Gross Amounts of Recognized Assets (1) Gross Amounts Not Offset In the Balance Sheets Financial Instruments Cash Collateral Received (Millions) Net Amount December 31, 2016 Derivatives $ — $ 17 $ — $ 17 Total $ — $ 17 $ — $ 17 December 31, 2015 Derivatives $ 20 $ 12 $ (17 ) $ 15 Total $ 20 $ 12 $ (17 ) $ 15 (1) There were no amounts offset in our balance sheets at December 31, 2016 or December 31, 2015 .
Offsetting Liabilities	Financial liabilities, including derivative liabilities, subject to offsetting and enforceable master netting arrangements as of December 31, 2016 and December 31, 2015 were as follows: Gross Amounts of Recognized Liabilities (1) Gross Amounts Not Offset In the Balance Sheets Financial Instruments Cash Collateral Paid (Millions) Net Amount December 31, 2016 Derivatives $ — $ — $ — $ — Total $ — $ — $ — $ — December 31, 2015 Derivatives $ 88 $ — $ (90 ) $ (2 ) Total $ 88 $ — $ (90 ) $ (2 ) (1) There were no amounts offset in our balance sheets at December 31, 2016 or December 31, 2015 .

Goodwill and Other Acquired I31

Goodwill and Other Acquired Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Change in Goodwill	The change in the carrying amount of goodwill for our reportable segments for the years ended December 31, 2016 and 2015 was as follows: (Millions) Health Care Group Insurance Total Company Balance at January 1, 2015 $ 10,500 $ 113 $ 10,613 Acquisitions 12 — 12 Dispositions — — — Subsequent adjustments 12 — 12 Balance at December 31, 2015 10,524 113 10,637 Acquisitions — — — Dispositions — — — Subsequent adjustments — — — Balance at December 31, 2016 $ 10,524 $ 113 $ 10,637
Other acquired intangible assets	Other acquired intangible assets at December 31, 2016 and 2015 were comprised of the following: (Millions) Cost Accumulated Amortization Net Balance Amortization Period (Years) 2016 Provider networks $ 1,254 $ 694 $ 560 12-25 (1) Customer lists 1,166 485 681 3-14 (1) Value of business acquired 149 92 57 20 Technology 176 123 53 4-10 Other 10 4 6 10-15 Definite-lived trademarks 170 107 63 5-20 Indefinite-lived trademarks 22 — 22 Total other acquired intangible assets $ 2,947 $ 1,505 $ 1,442 2015 Provider networks $ 1,254 $ 632 $ 622 12-25 (1) Customer lists 1,165 374 791 5-14 (1) Value of business acquired 149 80 69 20 Technology 176 93 83 4-10 Other 10 3 7 2-15 Definite-lived trademarks 170 76 94 5-20 Indefinite-lived trademarks 22 — 22 Total other acquired intangible assets $ 2,946 $ 1,258 $ 1,688 (1) The amortization period for our provider networks and customer lists includes an assumption of renewal or extension of these arrangements. At both December 31, 2016 and 2015 , the periods prior to the next renewal or extension for our provider networks primarily ranged from 1 to 3 years, and the period prior to the next renewal or extension for our customer lists was 1 year. Any costs related to the renewal or extension of these contracts are expensed as incurred.
Estimated annual pretax amortization for other acquired intangible assets over the next five years	We estimate annual pre-tax amortization for other acquired intangible assets over the next five years to be as follows: (Millions) 2017 $ 234 2018 198 2019 192 2020 180 2021 156

Health Care and Other Insuran32

Health Care and Other Insurance Liabilities (Tables)	12 Months Ended
	Dec. 31, 2016
Health Care [Member]
Short-duration Insurance Contracts, Claims Development [Table Text Block]	The information about incurred and paid Health Care claims development for the year ended December 31, 2015 is presented as required unaudited supplemental information. Incurred Health Care Claims, Net of Reinsurance (Millions) For the Years Ended December 31, Date of Service 2015 2016 (Unaudited) 2015 $ 41,825 $ 41,114 2016 44,110 Total $ 85,224 Cumulative Paid Health Care Claims, Net of Reinsurance (Millions) For the Years Ended December 31, Date of Service 2015 2016 (Unaudited) 2015 $ 35,735 $ 40,947 2016 37,888 Total $ 78,835 All outstanding liabilities for health care costs payable prior to 2015, net of reinsurance 66 Total outstanding liabilities for health care costs payable, net of reinsurance $ 6,455
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Table Text Block]	The reconciliation of the December 31, 2016 Health Care net incurred and paid claims development tables to the health care costs payable liability in the consolidated balance sheet is as follows: (Millions) December 31, 2016 Short-duration health care costs payable, net of reinsurance $ 6,455 Reinsurance recoverables 5 Insurance lines other than short duration 98 Total health care costs payable $ 6,558
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block]	The following table shows the components of the change in health care costs payable during 2016 , 2015 and 2014 : (Millions) 2016 2015 2014 Health care costs payable, beginning of the period $ 6,306 $ 5,621 $ 4,547 Less: Reinsurance recoverables 4 6 8 Health care costs payable, beginning of the period, net 6,302 5,615 4,539 Acquisition of businesses — — 29 Add: Components of incurred health care costs Current year 45,019 42,553 41,328 Prior years (764 ) (841 ) (581 ) Total incurred health care costs 44,255 41,712 40,747 Less: Claims paid Current year 38,700 36,389 35,851 Prior years 5,304 4,636 3,849 Total claims paid 44,004 41,025 39,700 Health care costs payable, end of period, net 6,553 6,302 5,615 Add: Reinsurance recoverables 5 4 6 Health care costs payable, end of period $ 6,558 $ 6,306 $ 5,621
Group Insurance [Member]
Short-duration Insurance Contracts, Claims Development [Table Text Block]	At December 31, 2016, we have disclosed six years of claims development and will add one year going forward in each subsequent year until we reach ten years of disclosure. Incurred Long-Term Disability Claims, Net of Reinsurance For the Years Ended December 31, As of December 31, 2016 (Millions) (Unaudited) Total IBNR liabilities plus expected development on reported claims Cumulative number of reported claims (Actual) Date of Service 2011 2012 2013 2014 2015 2016 2011 $ 360 $ 346 $ 335 $ 338 $ 342 $ 340 $ 2 6,988 2012 413 394 385 381 384 1 8,171 2013 473 482 463 478 2 10,104 2014 512 490 481 8 11,622 2015 533 504 18 12,924 2016 573 270 11,464 Total $ 2,760 Cumulative Paid Long-Term Disability Claims, Net of Reinsurance (Millions) For the Years Ended December 31, (Unaudited) Date of Service 2011 2012 2013 2014 2015 2016 2011 $ 20 $ 96 $ 144 $ 173 $ 199 $ 219 2012 24 119 177 208 236 2013 32 151 224 264 2014 35 161 242 2015 40 181 2016 48 Total 1,190 All outstanding unpaid long-term disability claims prior to 2011, net of reinsurance 754 Total outstanding unpaid long-term disability claims, net of reinsurance $ 2,324
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Table Text Block]	The reconciliation of the December 31, 2016 short-duration long-term disability net incurred and paid claims development tables to the short-duration long-term disability unpaid claims liability is as follows: December 31, 2016 Short-duration long-term disability unpaid claims, net of reinsurance $ 2,324 Reinsurance recoverables 26 Impact of discounting (446 ) Total short-duration long-term disability unpaid claims $ 1,904
Unpaid Claims Liabilities Presented at Present Value [Table Text Block]	The following is information on long-term disability unpaid claims liabilities presented at present value: Unpaid Long-Term Disability Claims Liabilities Presented at Present Value Carrying amount of unpaid claims liabilities Discount rate Aggregate amount of discount As of December 31, As of December 31, As of December 31, (Millions) 2016 2015 2016 2015 2016 2015 Long-term disability $ 1,878 $ 1,793 5.0 % 5.4 % $ 446 $ 473
Short-duration Insurance Contracts, Schedule of Historical Claims Duration [Table Text Block]	The following is required unaudited supplementary information about average historical long-term disability claims duration as of December 31, 2016: Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance (Unaudited) Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Long-term disability 7.3 % 25.3 % 15.0 % 8.2 % 6.9 % 5.8 %
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block]	The following table shows the components of the change in unpaid long-term disability claims during 2016, 2015 and 2014: (Millions) 2016 2015 2014 Long-term disability unpaid claims beginning of the period $ 1,819 $ 1,772 $ 1,685 Less: Reinsurance recoverables 27 27 28 Long-term disability unpaid claims, beginning of the period, net 1,792 1,745 1,657 Add: Components of incurred claims Current year 529 488 465 Prior years 41 (4 ) 22 Total incurred claims 570 484 487 Less: Claims paid Current year 48 40 35 Prior years 436 397 364 Total claims paid 484 437 399 Long-term disability unpaid claims, end of period, net 1,878 1,792 1,745 Add: Reinsurance recoverables 26 27 27 Long-term disability unpaid claims, end of period $ 1,904 $ 1,819 $ 1,772
Reconciliation to Total Unpaid Claims Liability [Table Text Block]	The reconciliation of the short-duration long-term disability unpaid claims liability to the total unpaid claims liability in the consolidated balance sheet is as follows for 2016 , 2015 and 2014 : (Millions) 2016 2015 2014 Short duration long-term disability unpaid claims $ 1,904 $ 1,819 $ 1,772 Term life unpaid claims 481 493 518 Other unpaid claims 119 116 106 Total unpaid claims $ 2,504 $ 2,428 $ 2,396

The ACA's Reinsurance, Risk A33

The ACA's Reinsurance, Risk Adjustment and Risk Corridor (Tables)	12 Months Ended
	Dec. 31, 2016
Health Care Reform [Abstract]
Health Care Reform Programs [Table Text Block]	Our current net receivable (payable) related to the 3Rs risk management programs at December 31, 2016 and 2015 was as follows: At December 31, 2016 At December 31, 2015 (Millions) Reinsurance Risk Adjustment Risk Corridor Reinsurance Risk Adjustment Risk Corridor Total current net receivable (payable) $ 202 $ (690 ) $ (10 ) $ 395 $ (710 ) $ (8 )

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Carrying Value of Long-Term Debt	The carrying value of our long-term debt at December 31, 2016 and 2015 was as follows: (Millions) 2016 2015 Senior notes, 5.95% due March 2017 (1) $ 386 $ 402 Senior notes, 1.75% due May 2017 (1) 250 249 Senior notes, 1.5% due November 2017 (1) 499 498 Senior notes, floating rate due December 2017 (1) 499 — Senior notes, 1.7% due June 2018 997 — Senior notes, 2.2% due March 2019 374 373 Senior notes, 1.9% due June 2019 1,642 — Senior notes, 3.95% due September 2020 745 743 Senior notes, 2.4% due June 2021 1,839 — Senior notes, 5.45% due June 2021 661 675 Senior notes, 4.125% due June 2021 495 494 Senior notes, 2.75% due November 2022 986 983 Senior notes, 2.8% due June 2023 1,290 — Senior notes, 3.5% due November 2024 742 741 Senior notes, 3.2% due June 2026 2,771 — Senior notes, 4.25% due June 2036 1,480 — Senior notes, 6.625% due June 2036 765 765 Senior notes, 6.75% due December 2037 527 527 Senior notes, 4.5% due May 2042 478 477 Senior notes, 4.125% due November 2042 489 489 Senior notes, 4.75% due March 2044 371 371 Senior notes, 4.375% due June 2046 2,375 — Total long-term debt 20,661 7,787 Less current portion of long-term debt 1,634 — Less credit facility issuance costs — 2 Total long-term debt, less current portion and credit facility issuance costs $ 19,027 $ 7,785 (1) At December 31, 2016 , our 5.95% senior notes due March 2017, 1.75% senior notes due May 2017, 1.5% senior notes due November 2017 and floating rate senior notes due December 2017 are each classified as current in our consolidated balance sheet.
Schedule of Maturities of Long-term Debt [Table Text Block]	At December 31, 2016 the amount of future maturities of our long-term debt are as follows: (Millions) 2017 $ 1,634 2018 997 2019 2,016 2020 745 2021 2,995 Thereafter 12,274

Pension and Other Postretirem35

Pension and Other Postretirement Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Schedule Of Changes In Benefit Obligations During Period	The following table shows the changes in the benefit obligations during 2016 and 2015 for our pension and OPEB plans: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Benefit obligation, beginning of year $ 5,946 $ 6,505 $ 257 $ 277 Interest cost 260 261 11 11 Actuarial loss (gain) 161 (453 ) — (10 ) Benefits paid (335 ) (367 ) (20 ) (21 ) Benefit obligation, end of year $ 6,032 $ 5,946 $ 248 $ 257
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits	The following table reconciles the beginning and ending balances of the fair value of plan assets during 2016 and 2015 for our pension and OPEB plans: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Fair value of plan assets, beginning of year $ 5,802 $ 6,147 $ 55 $ 58 Actual return on plan assets 426 — 1 1 Employer contributions 21 22 16 17 Benefits paid (335 ) (367 ) (20 ) (21 ) Fair value of plan assets, end of year $ 5,914 $ 5,802 $ 52 $ 55
Funded Status	The funded status of our pension and OPEB plans at the measurement date for 2016 and 2015 was as follows: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Benefit obligation $ (6,032 ) $ (5,946 ) $ (248 ) $ (257 ) Fair value of plan assets 5,914 5,802 52 55 Funded status $ (118 ) $ (144 ) $ (196 ) $ (202 )
Funded Status for Aetna and Non-qualified Pension Plans	At December 31, 2016 , the fair value of plan assets of the Aetna Pension Plan was in excess of the benefit obligations, while the Non-qualified Pension Plan had benefit obligations in excess of the fair value of plan assets. Below is the funded status of each of our Pension Plans: Aetna Pension Plan Non-qualified Pension Plan (Millions) 2016 2015 2016 2015 Benefit obligation $ (5,807 ) $ (5,714 ) $ (225 ) $ (232 ) Fair value of plan assets 5,914 5,802 — — Funded status $ 107 $ 88 $ (225 ) $ (232 )
Amounts in OCI not yet recognized for pension and OPEB plans	The amounts in accumulated other comprehensive loss that have not yet been recognized in net periodic benefit cost as of December 31, 2016 and 2015 were as follows: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Unrecognized prior service credit $ — $ (1 ) $ (19 ) $ (22 ) Unrecognized net actuarial losses 2,460 2,398 66 67 Amount recognized in accumulated other comprehensive loss $ (2,460 ) $ (2,397 ) $ (47 ) $ (45 )
Net Amount Of Liabilities Recognized Table	The (liabilities) assets recognized on our balance sheets at December 31, 2016 and 2015 for our pension and OPEB plans were comprised of the following: Pension Plans OPEB Plans (Millions) 2016 2015 2016 2015 Accrued benefit assets reflected in other long-term assets $ 107 $ 88 $ — $ — Accrued benefit liabilities reflected in other current liabilities (20 ) (19 ) (13 ) (14 ) Accrued benefit liabilities reflected in other long-term liabilities (205 ) (213 ) (183 ) (188 ) Net amount of (liabilities) assets recognized at December 31, $ (118 ) $ (144 ) $ (196 ) $ (202 )
Schedule of Net Benefit Costs	Components of the net periodic benefit (income) cost of our defined benefit pension plans and OPEB plans for the years ended December 31, 2016 , 2015 and 2014 were as follows: Pension Plans OPEB Plans (Millions) 2016 2015 2014 2016 2015 2014 Amortization of prior service credit $ — $ (1 ) $ (1 ) $ (4 ) $ (4 ) $ (4 ) Interest cost 260 261 288 11 11 12 Expected return on plan assets (389 ) (419 ) (422 ) (3 ) (3 ) (3 ) Recognized net actuarial losses 61 62 47 3 3 1 Settlement charge — — 112 — — — Net periodic benefit (income) cost $ (68 ) $ (97 ) $ 24 $ 7 $ 7 $ 6
Weighted Average Assumptions Table	The weighted average assumptions used to determine net periodic benefit (income) cost in 2016 , 2015 and 2014 for the pension and OPEB plans were as follows: Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Discount rate 4.50 % 4.12 % 4.96 % 4.39 % 4.02 % 4.73 % Expected long-term return on plan assets 6.90 % 7.00 % 7.00 % 4.75 % 5.30 % 5.30 %
Expected Benefits Payments Table	Expected benefit payments, which reflect future employee service, as appropriate, of the pension and OPEB plans to be paid for each of the next five years and in the aggregate for the next five years thereafter at December 31, 2016 were as follows: (Millions) Pension Plans OPEB Plans 2017 $ 495 $ 18 2018 360 18 2019 360 18 2020 362 18 2021 366 17 2022-2026 1,844 82
Fair Value Of Plan Assets	Pension Assets with changes in fair value measured on a recurring basis at December 31, 2016 were as follows: (Millions) Level 1 Level 2 Level 3 Total Debt securities: U.S. government securities $ 460 $ 122 $ — $ 582 States, municipalities and political subdivisions — 128 — 128 U.S. corporate securities — 1,291 — 1,291 Foreign securities — 103 — 103 Residential mortgage-backed securities — 163 — 163 Commercial mortgage-backed securities — 57 — 57 Other asset-backed securities — 60 — 60 Redeemable preferred securities — 6 — 6 Total debt securities 460 1,930 — 2,390 Equity securities: U.S. Domestic 1,305 5 — 1,310 International 611 — — 611 Domestic real estate 34 — — 34 Total equity securities 1,950 5 — 1,955 Other investments: Real estate — — 478 478 Common/collective trusts (1) — 465 — 465 Total other investments — 465 478 943 Total pension investments (2) $ 2,410 $ 2,400 $ 478 $ 5,288 (1) The assets in the underlying funds of common/collective trusts are comprised of $307 million of equity securities and $158 million of debt securities. (2) Excludes $180 million of cash and cash equivalents and other payables. Pension Assets with changes in fair value measured on a recurring basis at December 31, 2015 were as follows: (Millions) Level 1 Level 2 Level 3 Total Debt securities: U.S. government securities $ 428 $ 135 $ — $ 563 States, municipalities and political subdivisions — 126 — 126 U.S. corporate securities — 1,229 2 1,231 Foreign securities — 136 — 136 Residential mortgage-backed securities — 196 — 196 Commercial mortgage-backed securities — 51 1 52 Other asset-backed securities — 40 — 40 Redeemable preferred securities — 7 — 7 Total debt securities 428 1,920 3 2,351 Equity securities: U.S. Domestic 1,222 5 — 1,227 International 547 — — 547 Domestic real estate 28 — — 28 Total equity securities 1,797 5 — 1,802 Other investments: Real estate — — 497 497 Common/collective trusts (1) — 556 — 556 Total other investments — 556 497 1,053 Total pension investments (2) $ 2,225 $ 2,481 $ 500 $ 5,206 (1) The assets in the underlying funds of common/collective trusts are comprised of $302 million of equity securities and $254 million of debt securities. (2) Excludes $133 million of cash and cash equivalents and other payables.
Schedule of changes in the fair value of level three plan assets by asset category	The changes in the balances of Level 3 Pension Assets during 2016 and 2015 were as follows: 2016 (Millions) Real Estate Other Total Beginning balance $ 497 $ 3 $ 500 Actual return on plan assets 42 — 42 Purchases, sales and settlements (61 ) (1 ) (62 ) Transfers out of Level 3 — (2 ) (2 ) Ending balance $ 478 $ — $ 478 2015 (Millions) Real Estate Other Total Beginning balance $ 470 $ 2 $ 472 Actual return on plan assets 46 — 46 Purchases, sales and settlements (19 ) — (19 ) Transfers into Level 3 — 1 1 Ending balance $ 497 $ 3 $ 500
Asset Allocation And Target Asset Allocation Table	The actual and target asset allocations of the OPEB plans used at December 31, 2016 and 2015 presented as a percentage of total plan assets, were as follows: Target Target (Millions) 2016 Allocation 2015 Allocation Equity securities 11 % 5-15% 10 % 5-15% Debt securities 82 % 80-90% 83 % 80-90% Real estate/other 7 % 0-10% 7 % 0-10%

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The components of our income tax provision in 2016 , 2015 and 2014 were as follows: (Millions) 2016 2015 2014 Current taxes: Federal $ 1,662 $ 1,797 $ 1,233 State 129 112 84 Total current taxes 1,791 1,909 1,317 Deferred taxes (benefits): Federal (55 ) (59 ) 114 State (1 ) (9 ) 24 Total deferred income taxes (56 ) (68 ) 138 Total income taxes $ 1,735 $ 1,841 $ 1,455
Schedule of Effective Income Tax Rate Reconciliation	Income taxes were different from the amount computed by applying the statutory federal income tax rate to income before income taxes as follows: 2016 2015 2014 (Millions) Amount Percent Amount Percent Amount Percent Amount at statutory rate $ 1,397 35.0 % $ 1,483 35.0 % $ 1,225 35.0 % Health insurer fee 293 7.3 % 300 7.1 % 212 6.1 % State income taxes 83 2.1 % 63 1.5 % 78 2.2 % Other, net (38 ) (.9 )% (5 ) (.1 )% (60 ) (1.7 )% Income taxes $ 1,735 43.5 % $ 1,841 43.5 % $ 1,455 41.6 %
Schedule of Deferred Tax Assets and Liabilities	The significant components of our net deferred tax liabilities at December 31, 2016 and 2015 were as follows: (Millions) 2016 2015 Deferred tax assets: Insurance reserves $ 231 $ 302 Reserve for anticipated future losses on discontinued products 225 268 Employee and postretirement benefits 196 220 Net operating losses 147 165 Severance and facilities 135 18 Investments, net 80 92 Debt fair value adjustments 23 33 Deferred revenue 21 21 Other 117 66 Gross deferred tax assets 1,175 1,185 Less: Valuation allowance 118 128 Deferred tax assets, net of valuation allowance 1,057 1,057 Deferred tax liabilities: Goodwill and other acquired intangible assets 814 863 Cumulative depreciation and amortization 185 231 Unrealized gains on investment securities 42 138 Other 20 2 Total gross deferred tax liabilities 1,061 1,234 Net deferred tax liabilities $ (4 ) $ (177 )

Stock-based Employee Incentiv37

Stock-based Employee Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Stock-based Employee Incentive Plans [Abstract]
Assumptions Used in Stock Appreciation Rights Granted [Table Text Block]	The SARs granted to certain employees during 2016 and 2015 and described above had an estimated grant date fair value per SAR of $34.33 and $32.13 , respectively. The grant date fair value was calculated using a modified Black-Scholes option pricing model using the following assumptions: 2016 2015 Expected term (in years) 7.11 6.48 Volatility 32.9 % 33.4 % Risk-free interest rate 1.52 % 1.81 % Dividend yield 0.91 % 1.13 % Initial price $ 103.45 $ 100.50
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Table Text Block]	We estimated the grant date fair value of the 2013 PSARs using a Monte Carlo simulation. The 2013 PSARs had a grant date per PSAR fair value of $18.64 . That grant date fair value was calculated using the following assumptions: Expected settlement period (in years) 6.12 Volatility 40.4 % Risk-free interest rate .6 % Dividend yield 1.25 % Initial price $ 64.25
Schedule of Share-based Compensation, Stock Options and Stock Appreciation Rights Award Activity	The stock option, SAR and PSAR transactions during 2016 , 2015 and 2014 were as follows: (Millions, except exercise price and remaining life) Number of Stock Options, SARs and PSARs Weighted Average Exercise Price Weighted Average Remaining Contractual Life Aggregate Intrinsic Value 2014 Outstanding, beginning of year 10.5 $ 43.27 3.5 $ 265 Granted 1.4 72.36 — — Exercised (3.7 ) 40.50 — 132 Expired or forfeited (.1 ) 46.94 — — Outstanding, end of year ( 1) 8.1 $ 49.37 4.2 $ 318 Exercisable, end of year 6.1 $ 42.86 2.6 $ 280 2015 Outstanding, beginning of year 8.1 $ 49.37 4.2 $ 318 Granted 2.0 101.41 — — Exercised (2.5 ) 43.90 — 155 Expired or forfeited (.2 ) 91.25 — — Outstanding, end of year ( 1) 7.4 $ 64.11 5.3 $ 325 Exercisable, end of year 4.1 $ 45.88 2.6 $ 252 2016 Outstanding, beginning of year 7.4 $ 64.11 5.3 $ 325 Granted 2.4 104.47 — — Exercised (1.4 ) 52.99 — 85 Expired or forfeited (.4 ) 83.25 — — Outstanding, end of year 8.0 $ 77.20 5.9 $ 373 Exercisable, end of year 4.3 $ 57.26 3.6 $ 287 (1) PSARs are included in this table in 2015 and 2014 at the maximum amount that could potentially vest
Schedule Of Share Based Compensation Shares Authorized Under Stock Option Plans And Stock Appreciation Rights By Exercise Price Range	The following is a summary of information regarding SARs outstanding at December 31, 2016 (millions, except remaining contractual life and exercise price): Outstanding Exercisable Range of Exercise Prices Number Outstanding Weighted Average Remaining Contractual Life (Years) Weighted Average Exercise Price Aggregate Intrinsic Value Number Exercisable Weighted Average Exercise Price Aggregate Intrinsic Value 20.00-30.00 (1) — 2.4 $ 24.97 $ 2 — $ 24.97 $ 2 30.00-40.00 1.1 2.1 32.11 98 1.1 32.11 98 40.00-50.00 .7 .4 45.55 53 .7 45.55 53 50.00-60.00 .8 1.1 50.70 59 .8 50.70 59 60.00-70.00 .5 6.6 64.25 30 .5 64.25 30 70.00-80.00 1.0 6.8 72.34 50 .6 72.34 31 100.00-110.00 3.6 8.6 102.36 79 .6 101.05 14 110.00-120.00 .3 9.2 115.29 2 — — — $20.00-$130.00 (2) 8.0 5.9 $ 77.20 $ 373 4.3 $ 57.26 $ 287 (1) The number of outstanding and exercisable SARs and PSARs with exercise prices between $20 and $30 rounded to zero. (2) The number of outstanding SARs with exercise prices between $80 and $100 and between $120 and $130 rounded to zero .
Activity Under Stock Option, Performance Stock Appreciation Rights, Stock Appreciation Rights Plans	During 2016 , 2015 and 2014 , the following activity occurred under the Plans: (Millions) 2016 2015 2014 Cash received from stock option exercises $ — $ 7 $ 32 Intrinsic value of stock options/SARs exercised and stock units vested 384 413 323 Tax benefits realized for the tax deductions from stock options and SARs exercised and stock units vested 77 101 87 Fair value of stock options, SARs, PSARs and stock units vested (1) 223 126 107 (1) The fair value represents the aggregate grant date fair value of the stock options, SARs, PSARs and stock units as of the respective grant dates.
Assumptions Used In Market Stock Units Granted	MSUs granted in 2014 had a weighted average per MSU grant date fair value of $74.99 . The weighted-average per MSU grant date fair value was calculated using the following assumptions: 2014 Volatility 26.4 % Risk-free interest rate .7 % Dividend yield 1.3 % Initial price $ 72.26
Summary Of Status Of Performance Stock Units And Restricted Stock Units	RSU, MSU and PSU transactions in 2016 , 2015 and 2014 were as follows (number of units in millions): 2016 2015 2014 RSUs, MSUs and PSUs Weighted Average Grant Date Fair Value RSUs, MSUs and PSUs Weighted Average Grant Date Fair Value RSUs, MSUs and PSUs Weighted Average Grant Date Fair Value RSUs, MSUs and PSUs at beginning of year 3.9 $ 73.40 5.1 $ 58.57 5.3 $ 48.82 Granted 2.1 98.60 1.8 100.52 2.7 71.88 Vested (2.7 ) 68.87 (2.6 ) 59.72 (2.5 ) 50.11 Forfeited (.4 ) 71.17 (.4 ) 70.94 (.4 ) 56.89 RSUs, MSUs and PSUs at end of year 2.9 $ 91.95 3.9 $ 73.40 5.1 $ 58.57

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Class of Stock Disclosures [Abstract]
Schedule of Board authorizations for common stock repurchases	The activity under Board authorized share repurchase programs in 2016 , 2015 and 2014 was as follows: Purchase Not to Exceed Shares Purchased 2016 2015 2014 (Millions) Shares Cost Shares Cost Shares Cost Authorization date: November 21, 2014 $ 1,000 — $ — — $ — — $ — February 28, 2014 1,000 — — 3.0 296 7.6 621 September 27, 2013 750 — — — — 8.3 597 Total repurchases N/A — $ — 3.0 $ 296 15.9 $ 1,218 Repurchase authorization remaining at December 31, N/A $ 1,083 N/A $ 1,083 N/A $ 1,379
Accelerated Share Repurchases [Table Text Block]	We completed the following accelerated share repurchase programs with repurchase periods during the years ended December 31, 2016 and 2015: Trade Date: Value of Repurchase Program (Millions) Repurchase Period Number of Shares Repurchased (Millions) March 2, 2015 $ 100.0 April 2015 0.9
Dividends declared	In 2016 and 2015 our Board declared the following cash dividends: Date Declared Dividend Amount Per Share Stockholders of Record Date Date Paid/ To be Paid Total Dividends (Millions) Year ended December 31, 2015 February 27, 2015 $ .25 April 9, 2015 April 24, 2015 $ 87 May 15, 2015 .25 July 16, 2015 July 31, 2015 87 September 25, 2015 .25 October 15, 2015 October 30, 2015 87 December 4, 2015 .25 January 14, 2016 January 29, 2016 87 Year ended December 31, 2016 February 19, 2016 $ .25 April 14, 2016 April 29, 2016 88 May 20, 2016 .25 July 14, 2016 July 29, 2016 88 September 30, 2016 .25 October 13, 2016 October 28, 2016 88 December 2, 2016 .25 January 12, 2017 January 27, 2017 88
Statutory Accounting Practices Disclosure [Table Text Block]	At December 31, 2016, these amounts were as follows: (Millions) Minimum statutory surplus required by regulators $ 3,738 Investments on deposit with regulatory bodies 561 Maximum dividend distributions permitted in 2016 without state approval 1,902 The combined statutory net income for the years ended and combined statutory capital and surplus at December 31, 2016 , 2015 and 2014 for our insurance and HMO subsidiaries were as follows: (Millions) 2016 2015 2014 Statutory net income $ 2,229 $ 2,186 $ 2,127 Statutory capital and surplus 10,413 9,883 9,406

Other Comprehensive (Loss) In39

Other Comprehensive (Loss) Income (Tables)	12 Months Ended
	Dec. 31, 2016
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive (Loss) Income	Shareholders’ equity included the following activity in accumulated other comprehensive loss in 2016 , 2015 and 2014 : At December 31, (Millions) 2016 2015 2014 Previously impaired debt securities: (1) Beginning of period balance $ 19 $ 35 $ 34 Net unrealized (losses) gains ($(31), $(69) and $1 pretax) (20 ) (45 ) 1 Less: Net reclassification of (losses) gains to earnings ($(26) and $(44)) (2) (17 ) (29 ) — Other comprehensive (loss) income (3 ) (16 ) 1 End of period balance 16 19 35 All other securities: Beginning of period balance 312 568 327 Net unrealized (losses) gains ($(12), $(490) and $365 pretax) (8 ) (318 ) 237 Less: Net reclassification of gains (losses) to earnings ($11, $(97) and $(7) pretax) (2) 7 (62 ) (4 ) Other comprehensive (loss) income (15 ) (256 ) 241 End of period balance 297 312 568 Derivatives and foreign currency: Beginning of period balance (74 ) $ (61 ) $ — Net unrealized losses ($(273), $(26) and $(90) pretax) (177 ) (17 ) (58 ) Less: Net reclassification of (losses) gains to earnings ($(25), $(6) and $4 pretax) (3) (16 ) (4 ) 3 Other comprehensive loss (161 ) (13 ) (61 ) End of period balance (235 ) (74 ) (61 ) Pension and OPEB plans: Beginning of period balance (1,587 ) (1,653 ) (1,273 ) Net unrealized net actuarial (losses) gains arising during the period ($(126), $41 and $(739) pretax) (82 ) 27 (481 ) Less: Net pension settlement charge ($(112) pretax) (4) — — (73 ) Less: Net amortization of net actuarial losses ($(64), $(64) and $(48) pretax) (4) (42 ) (42 ) (31 ) Less: Net amortization of prior service credit ($5, $4 and $4 pretax) (4) 3 3 3 Other comprehensive (loss) income (43 ) 66 (380 ) End of period balance (1,630 ) (1,587 ) (1,653 ) Total beginning of period accumulated other comprehensive loss (1,330 ) (1,111 ) (912 ) Total other comprehensive loss (222 ) (219 ) (199 ) Total end of period accumulated other comprehensive loss $ (1,552 ) $ (1,330 ) $ (1,111 ) (1) Represents specifically identified unrealized gains on the non-credit related component of impaired debt securities that we do not intend to sell and subsequent changes in the fair value of any previously impaired security. (2) Reclassifications out of accumulated other comprehensive income for specifically identified previously impaired debt securities and all other securities are reflected in net realized capital gains (losses) within the Consolidated Statements of Income. (3) Reclassifications out of accumulated other comprehensive income for specifically identified foreign currency gains (losses) and derivatives are reflected in net realized capital gains (losses) within the Consolidated Statements of Income, except for the specifically identified effective portion of derivatives related to interest rate swaps which are reflected in interest expense. Refer to Note 9 for additional information. (4) Reclassifications out of accumulated other comprehensive income for specifically identified pension and OPEB plan expenses are reflected in general and administrative expenses within the Consolidated Statements of Income. During 2014, our reclassifications out of accumulated other comprehensive income for the Aetna Pension Plan reflect a pension settlement charge of $73 million ( $112 million pretax). (Refer to Note 10 for additional information).

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Earnings Per Share	The computations of basic and diluted EPS for 2016 , 2015 and 2014 are as follows: (Millions, except per common share data) 2016 2015 2014 Net income attributable to Aetna $ 2,271 $ 2,390 $ 2,041 Weighted average shares used to compute basic EPS 351.3 349.3 355.5 Dilutive effect of outstanding stock-based compensation awards 3.0 3.3 3.6 Weighted average shares used to compute diluted EPS 354.3 352.6 359.1 Basic EPS $ 6.46 $ 6.84 $ 5.74 Diluted EPS $ 6.41 $ 6.78 $ 5.68
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The stock-based compensation awards excluded from the calculation of diluted EPS for 2016 , 2015 and 2014 are as follows: (Millions) 2016 2015 2014 Stock appreciation rights ("SARs") (1) .1 .5 .3 Other stock-based compensation awards (2) .7 .8 1.2 (1) SARs are excluded from the calculation of diluted EPS if the exercise price is greater than the average market price of Aetna common shares during the period (i.e., the awards are anti-dilutive). (2) Performance stock units ("PSUs"), certain market stock units ("MSUs") with performance conditions, and performance stock appreciation rights ("PSARs") are excluded from the calculation of diluted EPS if all necessary performance conditions have not been satisfied at the end of the reporting period (refer to Note 12 for additional information about PSARs).

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Reinsurance Recoverables [Table Text Block]	Reinsurance recoverables recorded at December 31, 2016 and 2015 were as follows: (Millions) Total Recoverables Reinsurer 2016 2015 Lincoln Life & Annuity Company of New York $ 444 $ 458 VOYA Retirement Insurance and Annuity Company 209 223 Affordable Care Act 202 395 All Other 164 138 Total $ 1,019 $ 1,214
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Text Block]	Direct, assumed and ceded health care premiums earned for the years ended December 31 were as follows: (Millions) 2016 2015 2014 Direct $ 54,062 $ 51,539 $ 49,497 Assumed 402 368 316 Ceded (348 ) (289 ) (251 ) Net health care premiums $ 54,116 $ 51,618 $ 49,562
Effects of Reinsurance [Table Text Block]	The impact of reinsurance on health care costs for the years ended December 31 were as follows: (Millions) 2016 2015 2014 Direct $ 44,341 $ 42,038 $ 40,980 Assumed 339 298 263 Ceded (425 ) (624 ) (496 ) Net health care costs $ 44,255 $ 41,712 $ 40,747

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Other Commitments [Table Text Block]	For 2017 through 2021, our future net minimum payments under non-cancelable leases and funding obligations relating to equity limited partnership investments, commercial mortgage loans and real estate partnerships were as following: (Millions) 2017 2018 2019 2020 2021 Future net minimum payments under non-cancelable leases $ 143 $ 121 $ 81 $ 47 $ 37 Funding requirements for equity limited partnership investments, commercial mortgage loans and real estate partnerships 177 127 94 56 37 Total $ 320 $ 248 $ 175 $ 103 $ 74

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Summarized financial information of segments	Summarized financial information of our segment operations (1) for 2016 , 2015 and 2014 were as follows: (Millions) Health Care Group Insurance Large Case Pensions Corporate Financing Total Company 2016 Revenue from external customers $ 59,860 $ 2,251 $ 48 $ — $ 62,159 Net investment income 458 226 226 — 910 Interest expense — — — 604 604 Depreciation and amortization expense 681 — — — 681 Income taxes (benefits) 1,856 26 44 (191 ) 1,735 Operating earnings (loss) (2) 2,948 124 14 (169 ) 2,917 2015 Revenue from external customers $ 57,203 $ 2,240 $ 42 $ — $ 59,485 Net investment income 408 238 271 — 917 Interest expense — — — 369 369 Depreciation and amortization expense 671 — — — 671 Income taxes (benefits) 1,908 38 (9 ) (96 ) 1,841 Operating earnings (loss) (2) 2,712 136 17 (148 ) 2,717 2014 Revenue from external customers $ 54,677 $ 2,214 $ 86 $ — $ 56,977 Net investment income 368 261 317 — 946 Interest expense — — — 334 334 Depreciation and amortization expense 627 2 — — 629 Income taxes (benefits) 1,587 57 1 (190 ) 1,455 Operating earnings (loss) (2) 2,377 171 21 (164 ) 2,405 (1) Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer. (2) Operating earnings (loss) excludes net realized capital gains or losses, amortization of other acquired intangible assets and the other items described in this Note 18.
Reconciliation of operating earnings to net income	A reconciliation of net income attributable to Aetna to operating earnings (1) in 2016 , 2015 and 2014 was as follows. (Millions) 2016 2015 2014 Net income attributable to Aetna $ 2,271 $ 2,390 $ 2,041 Transaction and integration-related costs 517 258 201 Restructuring costs 404 15 — Reduction of reserve for anticipated future losses on discontinued products (128 ) — — Litigation-related proceeds — (110 ) — Loss on early extinguishment of long-term debt — — 181 Pension settlement charge — — 112 Release of litigation-related reserve — — (103 ) Amortization of other acquired intangible assets 247 255 243 Net realized capital (gain) losses (86 ) 65 (80 ) Income tax benefit (308 ) (156 ) (190 ) Operating earnings $ 2,917 $ 2,717 $ 2,405 (1) In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance: • We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. • Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses. • In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products. • In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income. • In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes. • During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. • In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement. • The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
Revenues from external customers by product	Revenues from external customers by product in 2016 , 2015 and 2014 were as follows: (Millions) 2016 2015 2014 Health care premiums $ 54,116 $ 51,618 $ 49,562 Health care fees and other revenue 5,744 5,585 5,115 Group insurance premiums 2,143 2,139 2,110 Group insurance fees and other revenues 108 101 104 Large case pensions premiums 39 32 76 Large case pensions other revenue 9 10 10 Total revenue from external customers (1) (2) $ 62,159 $ 59,485 $ 56,977 (1) All within the U.S., except approximately $642 million , $1.3 billion and $1.2 billion in 2016 , 2015 and 2014 , respectively, which were derived from foreign customers. (2) Revenue from the U.S. federal government was approximately $20.5 billion , $17.8 billion and $16.5 billion in 2016 , 2015 and 2014 , respectively, in the Health Care and Group Insurance segments. These amounts exceeded 10 percent of our total revenue from external customers in each of 2016 , 2015 and 2014 .
Reconciliation of revenues from external customers to total revenues	The following is a reconciliation of revenue from external customers to total revenues included in our statements of income in 2016 , 2015 and 2014 : (Millions) 2016 2015 2014 Revenue from external customers $ 62,159 $ 59,485 $ 56,977 Net investment income 910 917 946 Net realized capital gains (losses) 86 (65 ) 80 Total revenue $ 63,155 $ 60,337 $ 58,003

Discontinued Products (Tables)

Discontinued Products (Tables)	12 Months Ended
	Dec. 31, 2016
Discontinued Products [Abstract]
Activity in the Reserve for Anticipated Future Losses	The activity in the reserve for anticipated future losses on discontinued products in 2016 , 2015 and 2014 was as follows (pretax): (Millions) 2016 2015 2014 Reserve, beginning of period $ 1,067 $ 1,015 $ 980 Operating (loss) income (34 ) (9 ) 6 Net realized capital gains 57 61 29 Reserve reduction (128 ) — — Reserve, end of period $ 962 $ 1,067 $ 1,015
Anticipated Runoff Of Discontinued Products Reserve Balance	The anticipated run-off of the discontinued products reserve balance at December 31, 2016 (assuming that assets are held until maturity and that the reserve run-off is proportional to the liability run-off) is as follows: (Millions) 2017 $ 54 2018 53 2019 51 2020 50 2021 48 Thereafter 706
Assets and Liabilities Supporting Discontinued Products	Assets and liabilities supporting discontinued products (1) at December 31, 2016 and 2015 were as follows: (Millions) 2016 2015 Assets: Debt and equity securities available for sale $ 1,913 $ 2,020 Mortgage loans 370 396 Other investments 646 643 Total investments 2,929 3,059 Other assets 104 129 Current and deferred income taxes — 21 Receivable from continuing products (2) 554 602 Total assets $ 3,587 $ 3,811 Liabilities: Future policy benefits $ 2,326 $ 2,494 Reserve for anticipated future losses on discontinued products 962 1,067 Current and deferred income taxes 42 — Other liabilities (3) 257 250 Total liabilities $ 3,587 $ 3,811 (1) Assets supporting the discontinued products are distinguished from assets supporting continuing products. (2) At the time of discontinuance, a receivable from Large Case Pensions’ continuing products was established on the discontinued products balance sheet. This receivable represented the net present value of anticipated cash shortfalls in the discontinued products, which will be funded from continuing products. Interest on the receivable is accrued at the discount rate that was used to calculate the reserve. The offsetting payable, on which interest is similarly accrued, is reflected in continuing products. Interest on the payable generally offsets investment income on the assets available to fund the shortfall. These amounts are eliminated in consolidation. (3) Net unrealized capital gains on the available-for-sale debt securities are included in other liabilities and are not reflected in consolidated shareholders’ equity.
Expected Runoff Of Single Premium Annuities And Guaranteed Investment Contracts Liabilities	At December 31, 2016 , the expected run-off of the SPA liabilities, including future interest, was as follows: (Millions) 2017 $ 348 2018 332 2019 316 2020 301 2021 285 Thereafter 3,540
Comparison Of Expected And Actual Runoff Of Single Premium Annuities And Guaranteed Investment Contracts Liabilities	The liability expected as of December 31, 1993 and the actual liability balances at December 31, 2016 , 2015 and 2014 for the GIC and SPA liabilities were as follows: Expected Actual (Millions) GIC SPA GIC SPA 2014 $ 12 $ 2,281 $ — $ 2,646 2015 10 2,112 — 2,494 2016 9 1,942 — 2,326

Quarterly Financial Data (Table

Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Quarterly Data (unaudited) (Millions, except per share and common stock data) First Second Third Fourth 2016 Total revenue $ 15,694 $ 15,952 $ 15,782 $ 15,727 Income before income taxes $ 1,289 $ 1,354 $ 1,073 $ 275 Income taxes (551 ) (561 ) (476 ) (147 ) Net income including non-controlling interests 738 793 597 128 Less: Net (loss) income attributable to non-controlling interests 1 2 (7 ) (11 ) Net income attributable to Aetna $ 737 $ 791 $ 604 $ 139 Net income attributable to Aetna per share - basic (1) $ 2.10 $ 2.25 $ 1.72 $ .40 Net income attributable to Aetna per share - diluted (1) 2.09 2.23 1.70 .39 2015 Total revenue $ 15,094 $ 15,241 $ 14,953 $ 15,049 Income before income taxes $ 1,366 $ 1,262 $ 1,023 $ 585 Income taxes (590 ) (527 ) (461 ) (263 ) Net income including non-controlling interests 776 735 562 322 Less: Net income (loss) attributable to non-controlling interests (1 ) 3 2 1 Net income attributable to Aetna $ 777 $ 732 $ 560 $ 321 Net income attributable to Aetna per share - basic (1) $ 2.22 $ 2.10 $ 1.60 $ .92 Net income attributable to Aetna per share - diluted (1) 2.20 2.08 1.59 .91 (1) Calculation of net income attributable to Aetna per share is based on weighted average shares outstanding during each quarter and, accordingly, the sum may not equal the total for the year.

Summary of Significant Accoun46

Summary of Significant Accounting Policies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)days	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Minimum days delinquent when a loan can be considered a problem loan (in days) | days	60
Deferred Policy Acquisition Costs	$ 412	$ 305
Property, Plant and Equipment, Gross	1,400	1,400
Accumulated depreciation	851	774
Depreciation	$ 125	$ 131	$ 137
Health Care Organization, Capitation Costs	4.00%	4.00%	5.00%
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 246
Minimum assumed interest rates on limited payment pension contracts on large case pension business (in hundredths)	0.80%	0.80%
Limited Payments Contracts Maximum	11.30%	11.30%
Minimum assumed interest rates on long-duration group life and long-term care contracts (in hundredths)	2.50%	2.50%
Maximum Assumed Interest Rates On Long Duration Group Life And Long Term Care Contracts	8.80%	8.80%
Minimum interest rate for group health and life contracts (in hundredths)	0.00%	0.00%
Maximum interest rate for group health and life contracts (in hundredths)	2.40%	2.70%
Minimum interest rate for pension and annuity investment contracts (in hundredths)	3.50%	3.50%
Maximum interest rate for pension and annuity investment contracts (in hundredths)	15.90%	14.70%
Policyholder funds - Health Savings Account	$ 1,700	$ 1,500
Premium Deficiency Reserve	85
Health Insurer Fee	837	857	$ 605
Reinsurance contribution under Health Care Reform	118	210	$ 336
Severance Costs	330
Unamortized Debt Issuance Expense		$ 43
Proceeds and Excess Tax Benefit from Share-based Compensation	$ 29
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Building Useful Life	10 years
Property, Plant and Equipment, Useful Life	3 years
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Building Useful Life	40 years
Property, Plant and Equipment, Useful Life	15 years
Cash proceeds from Humana-related debt [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash Equivalents, at Carrying Value	$ 13,000

Summary of Significant Accoun47

Summary of Significant Accounting Policies- Valuation and Allowance (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Allowance for Uncollectible Premiums Receivable [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Balance	$ 139	$ 146
Allowance for Trade Receivables [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Balance	$ 37	$ 20

Acquisitions, Terminated Acqu48

Acquisitions, Terminated Acquisition and Terminated Divestiture (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Business Acquisition Estimated Purchase Price	$ 37,000
Loss on Contract Termination	53
Long-term Debt	20,661	$ 7,787
Loss on Redemption of Notes	420
Debt Instrument Redemption, Premium	$ 100
Loss on Contract Termination, Percent of Total Costs	70.00%
Goodwill, Acquired During Period	$ 0	12
bSwift [Member]
Business Acquisition [Line Items]
Purchase price for an acquisition		$ 400
Goodwill, Acquired During Period			$ 329
Debt Issued for Humana Acquisition [Domain]
Business Acquisition [Line Items]
Debt Instrument, Face Amount	13,000
Long-term Debt	$ 10,200
Debt Instrument, Redemption Price, Percentage	101.00%
Humana [Member]
Business Acquisition [Line Items]
Loss on Contract Termination	$ 1,000

Investments (Details)

Investments (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Total Investments [Line Items]
Restricted Investments	$ 657	$ 690
Current	3,046	3,015
Long-term investments	21,833	21,665
Total investments	24,879	24,680
Debt And Equity Securities Available For Sale [Member]
Total Investments [Line Items]
Current	2,876	2,877
Long-term investments	18,866	18,446
Total investments	21,742	21,323
Mortgage Loans [Member]
Total Investments [Line Items]
Current	170	127
Long-term investments	1,341	1,427
Total investments	1,511	1,554
Other Investments [Member]
Total Investments [Line Items]
Current	0	11
Long-term investments	1,626	1,792
Total investments	$ 1,626	$ 1,803

Investments - Debt and Equity S

Investments - Debt and Equity Securities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	[1]	$ 21,151	$ 20,728
Gross Unrealized Gains	[1]	799	853
Gross Unrealized Losses	[1]	(208)	(258)
Fair Value	[1]	21,742	21,323
Supporting Discontinued And Experience Rated Products [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Gains		195	209
Gross Unrealized Losses		(35)	(68)
Fair Value		2,900	3,000
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		21,067	20,705
Gross Unrealized Gains		779	849
Gross Unrealized Losses		(206)	(252)
Fair Value		21,640	21,302
US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		1,643	1,804
Gross Unrealized Gains		51	69
Gross Unrealized Losses		0	(1)
Fair Value		1,694	1,872
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		5,047	4,890
Gross Unrealized Gains		152	244
Gross Unrealized Losses		(61)	(9)
Fair Value		5,138	5,125
U.S. corporate securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		8,145	7,982
Gross Unrealized Gains		385	340
Gross Unrealized Losses		(55)	(147)
Fair Value		8,475	8,175
Foreign Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		2,958	2,910
Gross Unrealized Gains		163	148
Gross Unrealized Losses		(33)	(61)
Fair Value		3,088	2,997
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		793	914
Gross Unrealized Gains		11	17
Gross Unrealized Losses		(9)	(6)
Fair Value		795	925
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		1,382	1,262
Gross Unrealized Gains		5	17
Gross Unrealized Losses	[2]	(39)	(9)
Fair Value		1,348	1,270
Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		1,077	910
Gross Unrealized Gains		7	3
Gross Unrealized Losses	[2]	(9)	(19)
Fair Value		1,075	894
Redeemable Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		22	33
Gross Unrealized Gains		5	11
Gross Unrealized Losses		0	0
Fair Value		27	44
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		84	23
Gross Unrealized Gains		20	4
Gross Unrealized Losses		(2)	(6)
Fair Value		$ 102	$ 21
[1]	Investment risks associated with our experience-rated and discontinued products generally do not impact our operating results (refer to Note 19 for additional information on our accounting for discontinued products). At December 31, 2016, debt and equity securities with a fair value of approximately $2.9 billion, gross unrealized capital gains of $195 million and gross unrealized capital losses of $35 million and, at December 31, 2015, debt and equity securities with a fair value of approximately $3.0 billion, gross unrealized capital gains of $209 million and gross unrealized capital losses of $68 million were included in total debt and equity securities, but support our experience-rated and discontinued products. Changes in net unrealized capital gains (losses) on these securities are not reflected in accumulated other comprehensive income.
[2]	At both December 31, 2016 and 2015, we held securities for which we previously recognized an immaterial amount of non-credit related impairments in accumulated other comprehensive loss. These securities each had an immaterial amount of net unrealized capital gains at December 31, 2016 and 2015, respectively.

Investments - Debt Securities b

Investments - Debt Securities by Maturity (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis		$ 1,380
Available-for-sale Securities, Debt Maturities [Abstract]
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis		6,604
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis		5,059
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis		4,772
Available-for-sale Securities, Amortized Cost Basis		21,067
Available-for-sale Securities	[1]	21,742	$ 21,323
Debt Securities [Member]
Available-for-sale Securities, Debt Maturities [Abstract]
Available-for-sale Securities		21,640	21,302
Available-for-sale Securities With Established Maturities [Member]
Available-for-sale Securities, Debt Maturities [Abstract]
Less than one year		1,394
One year through five years		6,758
After five years through ten years		5,162
Greater than ten years		5,108
Residential Mortgage Backed Securities [Member]
Available-for-sale Securities, Debt Maturities [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis		793
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value		$ 795
Weighted average duration of securities		4 years 318 days
Available-for-sale Securities		$ 795	925
Commercial Mortgage Backed Securities [Member]
Available-for-sale Securities, Debt Maturities [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis		1,382
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value		$ 1,348
Weighted average duration of securities		6 years 277 days
Available-for-sale Securities		$ 1,348	1,270
Other Asset-Backed Securities [Member]
Available-for-sale Securities, Debt Maturities [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis		1,077
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value		$ 1,075
Weighted average duration of securities		1 year 91 days
Available-for-sale Securities		$ 1,075	$ 894
[1]	Investment risks associated with our experience-rated and discontinued products generally do not impact our operating results (refer to Note 19 for additional information on our accounting for discontinued products). At December 31, 2016, debt and equity securities with a fair value of approximately $2.9 billion, gross unrealized capital gains of $195 million and gross unrealized capital losses of $35 million and, at December 31, 2015, debt and equity securities with a fair value of approximately $3.0 billion, gross unrealized capital gains of $209 million and gross unrealized capital losses of $68 million were included in total debt and equity securities, but support our experience-rated and discontinued products. Changes in net unrealized capital gains (losses) on these securities are not reflected in accumulated other comprehensive income.

Investments - Unrealized Loss P

Investments - Unrealized Loss Position (Details) $ in Millions		12 Months Ended
		Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	[1]	3,669	4,953
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	[1]	$ 7,413	$ 6,596
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	[1]	$ 180	$ 220
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	[1]	537	626
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	[1]	$ 453	$ 520
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	[1]	$ 28	$ 38
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	4,206	5,579
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 7,866	$ 7,116
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	208	258
Supporting Discontinued And Experience Rated Products [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		890	966
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		$ 35	$ 68
Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		3,667	4,942
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 7,410	$ 6,596
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ 180	$ 215
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		529	621
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 450	$ 518
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 26	$ 37
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	4,196	5,563
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 7,860	$ 7,114
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	206	$ 252
Debt Securities [Member] | Supporting Discontinued And Experience Rated Products [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		890
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		$ 35
US Government Agencies Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		26	48
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 39	$ 67
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ 0	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		1	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 1	$ 13
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 0	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	27	54
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 40	$ 80
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	$ 0	$ 0
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		865	286
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 2,228	$ 714
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ 58	$ 6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		37	42
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 75	$ 92
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 3	$ 3
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	902	328
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 2,303	$ 806
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	$ 61	$ 9
Domestic Corporate Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		1,428	2,751
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 2,277	$ 3,169
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ 44	$ 131
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		114	215
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 101	$ 144
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 11	$ 16
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	1,542	2,966
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 2,378	$ 3,313
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	$ 55	$ 147
Foreign Corporate Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		649	793
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 970	$ 1,102
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ 27	$ 50
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		62	82
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 76	$ 89
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 6	$ 11
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	711	875
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 1,046	$ 1,191
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	$ 33	$ 61
Residential Mortgage Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		188	212
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 455	$ 329
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ 8	$ 3
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		104	177
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 17	$ 89
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 1	$ 3
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	292	389
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 472	$ 418
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	$ 9	$ 6
Commercial Mortgage Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		285	226
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 1,038	$ 562
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ 39	$ 9
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		3	30
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 3	$ 24
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 0	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	288	256
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 1,041	$ 586
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	$ 39	$ 9
Other Asset-Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		226	626
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 403	$ 653
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ 4	$ 16
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		208	69
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 177	$ 67
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 5	$ 4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	434	695
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 580	$ 720
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	$ 9	$ 20
Equity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		2	11
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 3	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		$ 0	$ 5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		8	5
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 3	$ 2
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		$ 2	$ 1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	[1]	10	16
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 6	$ 2
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	$ 2	$ 6
[1]	At December 31, 2016 and 2015, debt and equity securities in an unrealized capital loss position of $35 million and $68 million, respectively, and with related fair value of $890 million and $966 million, respectively, related to experience-rated and discontinued products.

Investments - Unrealized Loss53

Investments - Unrealized Loss Position Maturities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	$ 7,866	$ 7,116
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	208	258
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	[1]	7,860	7,114
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	[1]	206	252
Supporting Remaining Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		6,970
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		171
Supporting Discontinued And Experience Rated Products [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		890	966
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		35	$ 68
Supporting Discontinued And Experience Rated Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		890
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		35
Maturing in Less than one Year [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		206
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		0
Maturing in Less than one Year [Member] | Supporting Remaining Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		201
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		0
Maturing in Less than one Year [Member] | Supporting Discontinued And Experience Rated Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		5
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		0
Maturing in One Through Five Years [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,153
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		29
Maturing in One Through Five Years [Member] | Supporting Remaining Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,083
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		28
Maturing in One Through Five Years [Member] | Supporting Discontinued And Experience Rated Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		70
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		1
Maturing After Five Years Through Ten Years [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,847
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		52
Maturing After Five Years Through Ten Years [Member] | Supporting Remaining Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,559
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		43
Maturing After Five Years Through Ten Years [Member] | Supporting Discontinued And Experience Rated Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		288
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		9
Maturing in Greater Than Ten Years [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,561
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		68
Maturing in Greater Than Ten Years [Member] | Supporting Remaining Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,244
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		51
Maturing in Greater Than Ten Years [Member] | Supporting Discontinued And Experience Rated Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		317
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		17
Residential Mortgage Backed Securities [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		472
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		9
Residential Mortgage Backed Securities [Member] | Supporting Remaining Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		456
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		8
Residential Mortgage Backed Securities [Member] | Supporting Discontinued And Experience Rated Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		16
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		1
Commercial Mortgage Backed Securities [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,041
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		39
Commercial Mortgage Backed Securities [Member] | Supporting Remaining Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		867
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		33
Commercial Mortgage Backed Securities [Member] | Supporting Discontinued And Experience Rated Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		174
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		6
Other Asset-Backed Securities [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		580
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		9
Other Asset-Backed Securities [Member] | Supporting Remaining Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		560
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		8
Other Asset-Backed Securities [Member] | Supporting Discontinued And Experience Rated Products [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		20
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		$ 1
[1]	At December 31, 2016 and 2015, debt and equity securities in an unrealized capital loss position of $35 million and $68 million, respectively, and with related fair value of $890 million and $966 million, respectively, related to experience-rated and discontinued products.

Investments - Mortgage Loans (D

Investments - Mortgage Loans (Details) - Commercial Real Estate [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Movement in Mortgage Loans on Real Estate [Roll Forward]
New mortgage loans	$ 190	$ 213
Mortgage loans fully repaid	173	163
Mortgage loans foreclosed	8	9
Mortgage Loans on Real Estate	1,511	1,554
Scheduled Mortgage Loan Principal Repayments [Abstract]
2,017	171
2,018	216
2,019	123
2,020	166
2,021	253
Thereafter	582
Category 1 [Member]
Movement in Mortgage Loans on Real Estate [Roll Forward]
Mortgage Loans on Real Estate	45	66
Category 2 to 4 [Member]
Movement in Mortgage Loans on Real Estate [Roll Forward]
Mortgage Loans on Real Estate	1,449	1,467
Categories 5 and 6 [Member]
Movement in Mortgage Loans on Real Estate [Roll Forward]
Mortgage Loans on Real Estate	17	21
Category 7 [Member]
Movement in Mortgage Loans on Real Estate [Roll Forward]
Mortgage Loans on Real Estate	$ 0	$ 0

Investments - Investment Income

Investments - Investment Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income		$ 949	$ 963	$ 985
Investment expenses		(39)	(46)	(39)
Net Investment Income	[1]	910	917	946
Debt Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income		772	794	801
Mortgage Loans [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income		95	91	108
Other Investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income		82	78	76
Supporting Discontinued And Experience Rated Products [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net Investment Income		$ 208	$ 248	$ 289
[1]	Net investment income includes $208 million, $248 million and $289 million for 2016, 2015 and 2014, respectively, related to investments supporting our experience-rated and discontinued products.

Investments - Realized Gains (D

Investments - Realized Gains (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		$ (30)	$ (64)	$ (5)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Net Realized Capital Gains Losses Excluding OTTI Losses On Securities		116	(1)	85
Realized Investment Gains (Losses)		86	(65)	80
Debt Securities [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
OTTI Losses On Securities		(24)	(63)
Proceeds On Sales	[1]	6,725	4,987	4,615
Gross Realized Capital Gains	[1]	155	83	109
Gross Realized Capital Losses	[1]	$ 61	$ 76	$ 36
[1]	The proceeds on sales and gross realized capital gains and losses exclude the impact of the sales of short-term debt securities which primarily relate to our investments in mutual funds. These investments were excluded from the disclosed amounts because they represent an immaterial amount of aggregate gross realized capital gains or losses and have a high volume of sales activity.

Investments - Variable Interest

Investments - Variable Interest Entities and non-controlling Interests (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Long-term investments	$ 21,833				$ 21,665				$ 21,833	$ 21,665
Assets of variable interest entities	65,037				68,427				65,037	68,427
Non-controlling interests	62				65				62	65
Net (loss) income attributable to non-controlling interests	(11)	$ (7)	$ 2	$ 1	1	$ 2	$ 3	$ (1)	(15)	5	$ 4
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	10,111				11,816				10,111	11,816
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Long-term investments	472				477				472	477
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Long-term investments	1,116				1,115				1,116	1,115
Hedge Funds [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Assets of variable interest entities	32,926				33,066				32,926	33,066
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	2,819				3,535				2,819	3,535
Private Equity Funds [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Assets of variable interest entities	25,368				28,552				25,368	28,552
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	2,354				3,236				2,354	3,236
Real Estate Funds [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Assets of variable interest entities	6,743				6,809				6,743	6,809
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	4,938				5,045				4,938	5,045
Hedge Funds [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Long-term investments	384				418				384	418
Private Equity Funds [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Long-term investments	454				443				454	443
Real Estate Funds [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Long-term investments	$ 278				$ 254				$ 278	$ 254

Financial Instruments - Fair Va

Financial Instruments - Fair Value Measurements (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	[1]	$ 21,742	$ 21,323
Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		21,640	21,302
US Government Agencies Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,694	1,872
US States and Political Subdivisions Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		5,138	5,125
Domestic Corporate Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		8,475	8,175
Foreign Corporate Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		3,088	2,997
Residential Mortgage Backed Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		795	925
Commercial Mortgage Backed Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,348	1,270
Other Asset-Backed Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,075	894
Redeemable Preferred Stock [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		27	44
Equity Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		102	21
Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Derivative Assets		0	20
Assets, Fair Value Disclosure		21,742	21,343
Liabilities, Fair Value Disclosure [Abstract]
Derivative liabilities		0	88
Fair Value, Measurements, Recurring | Level 1
Assets, Fair Value Disclosure [Abstract]
Derivative Assets		0	0
Assets, Fair Value Disclosure		1,573	1,673
Liabilities, Fair Value Disclosure [Abstract]
Derivative liabilities		0	0
Fair Value, Measurements, Recurring | Level 2
Assets, Fair Value Disclosure [Abstract]
Derivative Assets		0	20
Assets, Fair Value Disclosure		20,023	19,556
Liabilities, Fair Value Disclosure [Abstract]
Derivative liabilities		0	88
Fair Value, Measurements, Recurring | Level 3
Assets, Fair Value Disclosure [Abstract]
Derivative Assets		0	0
Assets, Fair Value Disclosure		146	114
Liabilities, Fair Value Disclosure [Abstract]
Derivative liabilities		0	0
Fair Value, Measurements, Recurring | Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		21,640	21,302
Fair Value, Measurements, Recurring | Debt Securities [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,514	1,671
Fair Value, Measurements, Recurring | Debt Securities [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		20,023	19,536
Fair Value, Measurements, Recurring | Debt Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		103	95
Fair Value, Measurements, Recurring | US Government Agencies Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,694	1,872
Fair Value, Measurements, Recurring | US Government Agencies Debt Securities [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,514	1,671
Fair Value, Measurements, Recurring | US Government Agencies Debt Securities [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		180	201
Fair Value, Measurements, Recurring | US Government Agencies Debt Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | US States and Political Subdivisions Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		5,138	5,125
Fair Value, Measurements, Recurring | US States and Political Subdivisions Debt Securities [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | US States and Political Subdivisions Debt Securities [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		5,137	5,124
Fair Value, Measurements, Recurring | US States and Political Subdivisions Debt Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1	1
Fair Value, Measurements, Recurring | Domestic Corporate Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		8,475	8,175
Fair Value, Measurements, Recurring | Domestic Corporate Debt Securities [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Domestic Corporate Debt Securities [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		8,395	8,111
Fair Value, Measurements, Recurring | Domestic Corporate Debt Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		80	64
Fair Value, Measurements, Recurring | Foreign Corporate Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		3,088	2,997
Fair Value, Measurements, Recurring | Foreign Corporate Debt Securities [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Foreign Corporate Debt Securities [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		3,067	2,972
Fair Value, Measurements, Recurring | Foreign Corporate Debt Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		21	25
Fair Value, Measurements, Recurring | Residential Mortgage Backed Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		795	925
Fair Value, Measurements, Recurring | Residential Mortgage Backed Securities [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Residential Mortgage Backed Securities [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		795	925
Fair Value, Measurements, Recurring | Residential Mortgage Backed Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Commercial Mortgage Backed Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,348	1,270
Fair Value, Measurements, Recurring | Commercial Mortgage Backed Securities [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Commercial Mortgage Backed Securities [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,348	1,270
Fair Value, Measurements, Recurring | Commercial Mortgage Backed Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Other Asset-Backed Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,075	894
Fair Value, Measurements, Recurring | Other Asset-Backed Securities [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Other Asset-Backed Securities [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1,075	894
Fair Value, Measurements, Recurring | Other Asset-Backed Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Redeemable Preferred Stock [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		27	44
Fair Value, Measurements, Recurring | Redeemable Preferred Stock [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Redeemable Preferred Stock [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		26	39
Fair Value, Measurements, Recurring | Redeemable Preferred Stock [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		1	5
Fair Value, Measurements, Recurring | Brokered Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		80	78
Fair Value, Measurements, Recurring | Equity Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		102	21
Fair Value, Measurements, Recurring | Equity Securities [Member] | Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		59	2
Fair Value, Measurements, Recurring | Equity Securities [Member] | Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		0	0
Fair Value, Measurements, Recurring | Equity Securities [Member] | Level 3
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		$ 43	$ 19
[1]	Investment risks associated with our experience-rated and discontinued products generally do not impact our operating results (refer to Note 19 for additional information on our accounting for discontinued products). At December 31, 2016, debt and equity securities with a fair value of approximately $2.9 billion, gross unrealized capital gains of $195 million and gross unrealized capital losses of $35 million and, at December 31, 2015, debt and equity securities with a fair value of approximately $3.0 billion, gross unrealized capital gains of $209 million and gross unrealized capital losses of $68 million were included in total debt and equity securities, but support our experience-rated and discontinued products. Changes in net unrealized capital gains (losses) on these securities are not reflected in accumulated other comprehensive income.

Financial Instruments - Unobser

Financial Instruments - Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers between Level 1 and Level 2	$ 0		$ 0
Gross transfers into level 3	0		1
Gross transfers out of level 3	(39)		(64)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers into (out of) Level 3	(39)		(63)
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	114		162
Included in earnings	(15)		(6)
Included in other comprehensive income	4		4
Other	3	[1]	(4)	[2]
Purchases	100		37
Sales	(16)		(6)
Settlements	(5)		(10)
Transfers into (out of) Level 3	(39)		(63)
Ending balance	146		114
Fair Value, Measurements, Recurring | Foreign Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	25		32
Included in earnings	0		0
Included in other comprehensive income	0		0
Other	0	[1]	(1)	[2]
Purchases	16		0
Sales	(8)		(5)
Settlements	(2)		(1)
Transfers into (out of) Level 3	(10)		0
Ending balance	21		25
Fair Value, Measurements, Recurring | U.S. corporate securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	64		58
Included in earnings	(15)		(6)
Included in other comprehensive income	(4)		2
Other	0	[1]	0	[2]
Purchases	41		11
Sales	(3)		(1)
Settlements	(3)		0
Transfers into (out of) Level 3	0		0
Ending balance	80		64
Fair Value, Measurements, Recurring | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	19		18
Included in earnings	0		0
Included in other comprehensive income	11		2
Other	3	[1]	(3)	[2]
Purchases	10		2
Sales	0		0
Settlements	0		0
Transfers into (out of) Level 3	0		0
Ending balance	43		19
Fair Value, Measurements, Recurring | Other Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	6		54
Included in earnings	0		0
Included in other comprehensive income	(3)		0
Other	0	[1]	0	[2]
Purchases	33		24
Sales	(5)		0
Settlements	0		(9)
Transfers into (out of) Level 3	(29)		(63)
Ending balance	2		6
Separate Accounts Transfers [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers between Level 1 and Level 2	$ 0		$ 0
[1]	Reflects realized and unrealized capital gains and losses on investments supporting our experience-rated and discontinued products, which do not impact our operating results.
[2]	Reflects realized and unrealized capital gains and losses on investments supporting our experience-rated and discontinued products, which do not impact our operating results.

Financial Instruments - Balance

Financial Instruments - Balance Sheet Grouping (Details) - Fair Value, Measurements, Nonrecurring [Member] - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans		$ 1,540	$ 1,599
Bank Loans, Fair Value		8	188
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Investment contracts with a fixed maturity		8	9
Investment contracts without a fixed maturity		364	351
Long-term debt		21,468	8,227
Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans		0	0
Bank Loans, Fair Value		0	0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Investment contracts with a fixed maturity		0	0
Investment contracts without a fixed maturity		0	0
Long-term debt		0	0
Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans		0	0
Bank Loans, Fair Value		0	180
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Investment contracts with a fixed maturity		0	0
Investment contracts without a fixed maturity		0	0
Long-term debt		21,468	8,227
Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans		1,540	1,599
Bank Loans, Fair Value		8	8
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Investment contracts with a fixed maturity		8	9
Investment contracts without a fixed maturity		364	351
Long-term debt		0	0
Investment Type [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Mortgage loans		1,511	1,554
Bank Loans, net		8	193
Cost Method Investments	[1]	35	35
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Investment contracts with a fixed maturity		8	9
Investment contracts without a fixed maturity		378	371
Long-term debt		$ 20,661	$ 7,785
[1]	It was not practical to estimate the fair value of these cost-method investments as it represents shares of unlisted companies.

Financial Instruments - Separat

Financial Instruments - Separate Accounts Fair Value (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		$ 3,991	$ 4,035
Fair Value, Measurements, Recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets	[1]	3,898	3,852
Fair Value, Measurements, Recurring | Level 1
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets	[1]	932	921
Fair Value, Measurements, Recurring | Level 2
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets	[1]	2,966	2,927
Fair Value, Measurements, Recurring | Level 3
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets	[1]	0	4
Cash and Cash Equivalents [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		93	183
Debt Securities [Member] | Fair Value, Measurements, Recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		3,144	3,137
Debt Securities [Member] | Fair Value, Measurements, Recurring | Level 1
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		766	751
Debt Securities [Member] | Fair Value, Measurements, Recurring | Level 2
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		2,378	2,382
Debt Securities [Member] | Fair Value, Measurements, Recurring | Level 3
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		0	4
Equity Securities [Member] | Fair Value, Measurements, Recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		172	175
Equity Securities [Member] | Fair Value, Measurements, Recurring | Level 1
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		166	170
Equity Securities [Member] | Fair Value, Measurements, Recurring | Level 2
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		6	5
Equity Securities [Member] | Fair Value, Measurements, Recurring | Level 3
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		0	0
Common/collective trusts | Fair Value, Measurements, Recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		582	540
Common/collective trusts | Fair Value, Measurements, Recurring | Level 1
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		0	0
Common/collective trusts | Fair Value, Measurements, Recurring | Level 2
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		582	540
Common/collective trusts | Fair Value, Measurements, Recurring | Level 3
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Accounts Assets		$ 0	$ 0
[1]	Excludes $93 million and $183 million of cash and cash equivalents and other receivables at December 31, 2016 and 2015, respectively.

Financial Instruments - Separ62

Financial Instruments - Separate Accounts Unobservable Inputs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers between Level 1 and Level 2	$ 0	$ 0
Separate Accounts Transfers [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers between Level 1 and Level 2	$ 0	$ 0

Financial Instruments - Balan63

Financial Instruments - Balance Sheet Offsetting (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	$ 0	$ 20
Derivative, Collateral, Obligation to Return Securities		17	12
Derivative, Collateral, Obligation to Return Cash		0	(17)
Derivative Asset, Fair Value, Amount Offset Against Collateral		17	15
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Gross	[1]	0	20
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Securities		17	12
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Cash		0	17
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Amount Offset Against Collateral		$ 17	$ 15
[1]	There were no amounts offset in our balance sheets at December 31, 2016 or December 31, 2015.

Financial Instruments Offsettin

Financial Instruments Offsetting Financial Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	[1]	$ 0	$ 88
Derivative, Collateral, Right to Reclaim Securities		0	0
Derivative, Collateral, Right to Reclaim Cash		0	(90)
Derivative Liability, Fair Value, Amount Offset Against Collateral		0	(2)
Total Gross Liabilities Recognized Subject to Offsetting	[1]	0	88
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Collateral, Right to Reclaim Securities		0	0
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Collateral, Right to Reclaim Cash		0	90
Derivative liabilities, net		$ 0	$ 2
[1]	There were no amounts offset in our balance sheets at December 31, 2016 or December 31, 2015.

Goodwill and Other Acquired I65

Goodwill and Other Acquired Intangible Assets - Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Balance, beginning of the period	$ 10,637	$ 10,613
Goodwill, Acquired During Period	0	12
Goodwill, Other Increase (Decrease)	0	0
Goodwill, Purchase Accounting Adjustments	0	12
Balance, end of the period	10,637	10,637
Health Care [Member]
Goodwill [Roll Forward]
Balance, beginning of the period	10,524	10,500
Goodwill, Acquired During Period	0	12
Goodwill, Other Increase (Decrease)	0	0
Goodwill, Purchase Accounting Adjustments	0	12
Balance, end of the period	10,524	10,524
Group Insurance [Member]
Goodwill [Roll Forward]
Balance, beginning of the period	113	113
Goodwill, Acquired During Period	0	0
Goodwill, Other Increase (Decrease)	0	0
Goodwill, Purchase Accounting Adjustments	0	0
Balance, end of the period	$ 113	$ 113

Goodwill and Other Acquired I66

Goodwill and Other Acquired Intangible Assets - Intangible Assets (Details) $ in Millions		12 Months Ended
		Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Other Acquired Intangible Assets[Line Items]
Acquired Finite-lived Intangible Asset, Weighted-Average Period before Renewal or Extension		1 year	1 year
Accumulated Amortization		$ 1,505	$ 1,258
Other acquired intangible assets, net		1,442	1,688
Intangible Assets, Gross (Excluding Goodwill)		2,947	2,946
Trademarks Indefinite Lived [Member]
Other Acquired Intangible Assets[Line Items]
Indefinite-lived trademarks		22	22
Indefinite-lived intangible asset, accumulated amortization		0	0
Provider networks [Member]
Other Acquired Intangible Assets[Line Items]
Cost		1,254	1,254
Accumulated Amortization		694	632
Other acquired intangible assets, net		$ 560	$ 622
The minimum number of years in the period prior to the next renewal or extension for provider networks (in years)		1	1
The maximum number of years in the period prior to the next renewal or extension for provider networks (in years)		3	3
Customer Lists [Member]
Other Acquired Intangible Assets[Line Items]
Cost		$ 1,166	$ 1,165
Accumulated Amortization		485	374
Other acquired intangible assets, net		681	791
Value Of Business Acquired [Member]
Other Acquired Intangible Assets[Line Items]
Cost		149	149
Accumulated Amortization		92	80
Other acquired intangible assets, net		57	69
Technology [Member]
Other Acquired Intangible Assets[Line Items]
Cost		176	176
Accumulated Amortization		123	93
Other acquired intangible assets, net		53	83
Other [Member]
Other Acquired Intangible Assets[Line Items]
Cost		10	10
Accumulated Amortization		4	3
Other acquired intangible assets, net		6	7
Trademarks Definite Lived [Member]
Other Acquired Intangible Assets[Line Items]
Cost		170	170
Accumulated Amortization		107	76
Other acquired intangible assets, net		$ 63	$ 94
Minimum [Member] | Provider networks [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life	[1]	12 years	12 years
Minimum [Member] | Customer Lists [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life	[1]	3 years	5 years
Minimum [Member] | Other [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life		10 years	2 years
Minimum [Member] | Trademarks Definite Lived [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life		5 years	5 years
Minimum [Member] | Technology-Based Intangible Assets [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life		4 years	4 years
Maximum [Member] | Provider networks [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life	[1]	25 years	25 years
Maximum [Member] | Customer Lists [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life	[1]	14 years	14 years
Maximum [Member] | Value Of Business Acquired [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life		20 years	20 years
Maximum [Member] | Other [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life		15 years	15 years
Maximum [Member] | Trademarks Definite Lived [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life		20 years	20 years
Maximum [Member] | Technology-Based Intangible Assets [Member]
Other Acquired Intangible Assets[Line Items]
Useful Life		10 years	10 years
[1]	The amortization period for our provider networks and customer lists includes an assumption of renewal or extension of these arrangements. At both December 31, 2016 and 2015, the periods prior to the next renewal or extension for our provider networks primarily ranged from 1 to 3 years, and the period prior to the next renewal or extension for our customer lists was 1 year. Any costs related to the renewal or extension of these contracts are expensed as incurred.

Goodwill and Other Acquired I67

Goodwill and Other Acquired Intangible Assets - Future Amortization Expense (Details) $ in Millions	Dec. 31, 2016USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,017	$ 234
2,018	198
2,019	192
2,020	180
2,021	$ 156

Health Care and Other Insuran68

Health Care and Other Insurance Liabilities Unpaid Claims (Health Care) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Health care costs payable	$ 6,558	$ 6,306
Health Care [Member]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	85,224
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	78,835
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	66
Health care costs payable, net of reinsurance	6,455
Reinsurance Recoverables on Unpaid Losses, Gross	5	4	$ 6	$ 8
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item	98
Health care costs payable	6,558	6,306	$ 5,621	$ 4,547
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	5,600
Short-duration Insurance Contracts, Accident Year 2015 [Member] | Health Care [Member]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	41,114	41,825
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	40,947	$ 35,735
Short-duration Insurance Contracts, Accident Year 2016 [Member] | Health Care [Member]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	44,110
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 37,888

Health Care and Other Insuran69

Health Care and Other Insurance Liabilities Reconciliation of Health Care Costs Payable (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Add: Components of incurred health care costs [Abstract]
Health care costs	[1]	$ 44,255	$ 41,712	$ 40,747
Less: Claims paid [Abstract]
Health care costs payable		6,558	6,306
Health Care [Member]
Liability for Unpaid Claims and Claims Adjustment Expense, Business Acquisitions		0	0	29
Add: Components of incurred health care costs [Abstract]
Current Year Claims and Claims Adjustment Expense		45,019	42,553	41,328
Prior Year Claims and Claims Adjustment Expense		(764)	(841)	(581)
Health care costs		44,255	41,712	40,747
Less: Claims paid [Abstract]
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year		38,700	36,389	35,851
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years		5,304	4,636	3,849
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid		44,004	41,025	39,700
Short-Duration Liability for Unpaid Claims		6,553	6,302	5,615	$ 4,539
Reinsurance Recoverables on Unpaid Losses, Gross		5	4	6	8
Health care costs payable		$ 6,558	$ 6,306	$ 5,621	$ 4,547
[1]	Health care costs have been reduced by Insured member co-payments related to our mail order and specialty pharmacy operations of $115 million, $117 million and $107 million for 2016, 2015 and 2014, respectively.

Health Care and Other Insuran70

Health Care and Other Insurance Liabilities Unpaid Claims (Other Liabilities) (Details) - Group Insurance [Member] $ in Millions	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 2,760
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,190
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	754
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	2,324
Reinsurance Recoverables on Unpaid Losses, Gross	26	$ 27	$ 27	$ 28
Short-duration Insurance Contracts, Discounted Liabilities, Aggregate Discount	(446)	(473)
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	1,904	1,819	1,772	1,685
Short-duration Insurance Contracts, Accident Year 2011 [Member]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	340	342	338	335	$ 346	$ 360
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2
Short-duration Insurance Contracts, Number of Reported Claims	6,988
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 219	199	173	144	96	$ 20
Short-duration Insurance Contracts, Accident Year 2012 [Member]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	384	381	385	394	413
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1
Short-duration Insurance Contracts, Number of Reported Claims	8,171
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 236	208	177	119	$ 24
Short-duration Insurance Contracts, Accident Year 2013 [Member]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	478	463	482	473
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2
Short-duration Insurance Contracts, Number of Reported Claims	10,104
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 264	224	151	$ 32
Short-duration Insurance Contracts, Accident Year 2014 [Member]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	481	490	512
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 8
Short-duration Insurance Contracts, Number of Reported Claims	11,622
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 242	161	$ 35
Short-duration Insurance Contracts, Accident Year 2015 [Member]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	504	533
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 18
Short-duration Insurance Contracts, Number of Reported Claims	12,924
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 181	$ 40
Short-duration Insurance Contracts, Accident Year 2016 [Member]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	573
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 270
Short-duration Insurance Contracts, Number of Reported Claims	11,464
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 48

Health Care and Other Insuran71

Health Care and Other Insurance Liabilities Present Value Information (Other Liabilities) (Details) - Group Insurance [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-Duration Contracts, Discounted Liabilities, Amount	$ 1,878	$ 1,793
Short-Duration Contracts, Discounted Liabilities, Discount Rate	5.00%	5.40%
Short-duration Insurance Contracts, Discounted Liabilities, Aggregate Discount	$ 446	$ 473
Short-duration Insurance Contracts, Discounted Liabilities, Interest Accretion	$ 97	$ 97	$ 93

Health Care and Other Insuran72

Health Care and Other Insurance Liabilities Claims Duration (Other Liabilities) (Details)	Dec. 31, 2016
Short-Duration Insurance Contracts [Abstract]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	7.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	25.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	15.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	8.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	6.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	5.80%

Health Care and Other Insuran73

Health Care and Other Insurance Liabilities Reconciliation of Other Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Add Claims Incurred for Other Liabilities [Roll Forward]
Policyholder Benefits and Claims Incurred, Net, Other	$ 2,101	$ 2,121	$ 2,165
Group Insurance [Member]
Add Claims Incurred for Other Liabilities [Roll Forward]
Current Year Claims and Claims Adjustment Expense	529	488	465
Prior Year Claims and Claims Adjustment Expense	41	(4)	22
Policyholder Benefits and Claims Incurred, Net, Other	570	484	487
Less: Claims paid [Abstract]
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	48	40	35
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	436	397	364
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	484	437	399
Short-Duration Liability for Unpaid Claims, Other Insurance	1,878	1,792	1,745	$ 1,657
Reinsurance Recoverables on Unpaid Losses, Gross	26	27	27	28
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	1,904	1,819	1,772	$ 1,685
Term Life Unpaid Claims	481	493	518
Other Unpaid Claims Liabilities	119	116	106
Total Liability for Unpaid Claims	$ 2,504	$ 2,428	$ 2,396

The ACA's Reinsurance, Risk A74

The ACA's Reinsurance, Risk Adjustment and Risk Corridor (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Health Care Reform [Abstract]
Reinsurance Recoverable Under Health Care Reform	$ 202	$ 395
Net health care reform risk adjustment payable (receivable)	(690)	(710)
Health care reform risk corridor net	(10)	$ (8)
Health care reform risk corridor receivable, gross	$ 465

Debt (Details)

Debt (Details)		3 Months Ended	12 Months Ended
		Mar. 31, 2016USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)Derivatives_and_swaps	Dec. 31, 2014USD ($)	Jun. 02, 2016USD ($)
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months			$ 1,634,000,000
Long-term Debt, Current Maturities			1,634,000,000	$ 0
Long-term debt, less current portion			19,027,000,000	7,785,000,000
Long-term Debt			20,661,000,000	7,787,000,000
Unamortized Debt Issuance Expense				43,000,000
Proceeds from Issuance of Long-term Debt			12,886,000,000	0	$ 1,482,000,000
Interest Rate Cash Flow Hedges [Abstract]
Loss on early extinguishment of long-term debt	[1]		0	0	$ (181,000,000)
Federal Home Loan Bank Advances			0	$ 0
Long-term Debt, Maturities, Repayments of Principal in Year Two			997,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Three			2,016,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Four			745,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Five			2,995,000,000
Long-term Debt, Maturities, Repayments of Principal after Year Five			12,274,000,000
Senior Notes, 6.0%, Due 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				6.00%
Early Repayment of Senior Debt				$ 750,000,000
Interest Rate Cash Flow Hedges [Abstract]
Loss on early extinguishment of long-term debt, net of tax				(60,000,000)
Loss on early extinguishment of long-term debt				(92,000,000)
Senior Notes, 5.95%, Due 2017 [Member]
Debt Instrument [Line Items]
Long-term Debt	[2]		$ 386,000,000	$ 402,000,000
Debt Instrument, Interest Rate, Stated Percentage			5.95%	5.95%
Senior Notes, 1.75%, Due 2017 [Member]
Debt Instrument [Line Items]
Long-term Debt	[2]		$ 250,000,000	$ 249,000,000
Debt Instrument, Interest Rate, Stated Percentage			1.75%	1.75%
Senior Notes, 1.5%, Due 2017 [Member]
Debt Instrument [Line Items]
Long-term Debt	[2]		$ 499,000,000	$ 498,000,000
Debt Instrument, Interest Rate, Stated Percentage			1.50%	1.50%
Variable Rate [Domain]
Debt Instrument [Line Items]
Long-term Debt	[2]		$ 499,000,000	$ 0
Debt Instrument, Face Amount			500,000,000
Senior Notes, 6.5%, Due 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				6.50%
Early Repayment of Senior Debt				$ 496,000,000
Interest Rate Cash Flow Hedges [Abstract]
Loss on early extinguishment of long-term debt, net of tax				(58,000,000)
Loss on early extinguishment of long-term debt				(89,000,000)
Senior Notes, 3.95%, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 745,000,000	$ 743,000,000
Debt Instrument, Interest Rate, Stated Percentage			3.95%	3.95%
Senior Notes, 2.4%, Due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 1,839,000,000	$ 0
Debt Instrument, Interest Rate, Stated Percentage			2.40%	2.40%
Debt Instrument, Face Amount			$ 1,900,000,000
Senior Notes, 2.8%, Due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 1,290,000,000	$ 0
Debt Instrument, Interest Rate, Stated Percentage			2.80%	2.80%
Debt Instrument, Face Amount			$ 1,300,000,000
Senior Notes, 5.45%, Due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 661,000,000	$ 675,000,000
Debt Instrument, Interest Rate, Stated Percentage			5.45%	5.45%
Senior Notes, 4.125%, Due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 495,000,000	$ 494,000,000
Debt Instrument, Interest Rate, Stated Percentage			4.125%	4.125%
Senior Notes, 2.75%, Due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 986,000,000	$ 983,000,000
Debt Instrument, Interest Rate, Stated Percentage			2.75%	2.75%
Senior notes, 3.5%, due 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 742,000,000	$ 741,000,000
Debt Instrument, Interest Rate, Stated Percentage			3.50%	3.50%
Proceeds from Issuance of Long-term Debt				$ 750,000,000
Senior Notes, 6.625%, Due 2036 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 765,000,000	$ 765,000,000
Debt Instrument, Interest Rate, Stated Percentage			6.625%	6.625%
Senior Notes, 6.75%, Due 2037 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 527,000,000	$ 527,000,000
Debt Instrument, Interest Rate, Stated Percentage			6.75%	6.75%
Senior Notes, 4.5% due 2042 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 478,000,000	$ 477,000,000
Debt Instrument, Interest Rate, Stated Percentage			4.50%	4.50%
Senior Notes, 4.125%, Due 2042 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 489,000,000	$ 489,000,000
Debt Instrument, Interest Rate, Stated Percentage			4.125%	4.125%
Senior Notes, 4.75%, Due 2044 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 371,000,000	$ 371,000,000
Debt Instrument, Interest Rate, Stated Percentage			4.75%	4.75%
Proceeds from Issuance of Long-term Debt				$ 375,000,000
Senior Notes, 4.375%, Due 2046 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 2,375,000,000	$ 0
Debt Instrument, Interest Rate, Stated Percentage			4.375%	4.375%
Debt Instrument, Face Amount			$ 2,400,000,000
Debt Issued for Humana Acquisition [Domain]
Debt Instrument [Line Items]
Long-term Debt			$ 10,200,000,000
Debt Instrument, Redemption Price, Percentage			101.00%
Debt Instrument, Face Amount			$ 13,000,000,000
Senior Notes, 1.7%, Due 2018 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 997,000,000	$ 0
Debt Instrument, Interest Rate, Stated Percentage			1.70%	1.70%
Debt Instrument, Face Amount				$ 1,000,000,000
Senior Notes, 2.2%, Due 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 374,000,000	$ 373,000,000
Debt Instrument, Interest Rate, Stated Percentage			2.20%	2.20%
Proceeds from Issuance of Long-term Debt				$ 375,000,000
Senior Notes, 1.9%, Due 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 1,642,000,000	$ 0
Debt Instrument, Interest Rate, Stated Percentage			1.90%	1.90%
Debt Instrument, Face Amount			$ 1,700,000,000
Senior notes, 3.2%, due 2026 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 2,771,000,000	$ 0
Debt Instrument, Interest Rate, Stated Percentage			3.20%	3.20%
Debt Instrument, Face Amount			$ 2,800,000,000
Senior notes, 4.25%, due 2036 [Member]
Debt Instrument [Line Items]
Long-term Debt			$ 1,480,000,000	$ 0
Debt Instrument, Interest Rate, Stated Percentage			4.25%	4.25%
Debt Instrument, Face Amount			$ 1,500,000,000
Debt refinance [Domain]
Interest Rate Cash Flow Hedges [Abstract]
Number of Interest Rate Derivatives Held | Derivatives_and_swaps				2
April 2014 Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Derivative, Cost of Hedge Net of Cash Received				$ 15,000,000
Gain on Cash Flow Hedge Ineffectiveness				3,000,000
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net				(12,000,000)
Derivative, Notional Amount				250,000,000
2012 Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Derivative, Cost of Hedge Net of Cash Received				34,000,000
Gain on Cash Flow Hedge Ineffectiveness				12,000,000
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net				22,000,000
Derivative, Notional Amount				375,000,000
2015 and 2016 Cash Flow Hedges [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount			3,500,000,000
March 2014 Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net			(73,000,000)
Derivative, Notional Amount			500,000,000
Reclassification out of Accumulated Other Comprehensive Income [Domain]
Debt Instrument [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net			(330,000,000)
Terminated Swaps [Member]
Debt Instrument [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net			(193,000,000)
Derivative, Counterparty Payment			193,000,000
Derivative, Notional Amount			2,300,000,000			$ 3,500,000,000
2015 and 2016 Cash Flow Hedge [Member]
Debt Instrument [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net			(51,000,000)
Derivative, Counterparty Payment			51,000,000
Treasury Rate Locks Issued Q2 2016 [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount			2,300,000,000
March 2014 Cash Flow Hedge [Domain]
Interest Rate Cash Flow Hedges [Abstract]
Loss on Cash Flow Hedge Ineffectiveness		$ 4,000,000
March 2014 Cash Flow Hedge [Member]
Debt Instrument [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net			(25,000,000)
Derivative, Counterparty Payment			103,000,000
Interest Rate Cash Flow Hedges [Abstract]
Loss on Cash Flow Hedge Ineffectiveness			2,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Expense			0	$ 2,000,000
Term Loan [Member]
Debt Instrument [Line Items]
Term Loan Principal			3,200,000,000
Bridge Loan [Member]
Debt Instrument [Line Items]
Expected Proceeds From Issuance Of Long Term Debt			$ 13,000,000,000
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
[2]	At December 31, 2016, our 5.95% senior notes due March 2017, 1.75% senior notes due May 2017, 1.5% senior notes due November 2017 and floating rate senior notes due December 2017 are each classified as current in our consolidated balance sheet.

Debt Debt Maturities (Details)

Debt Debt Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Long-Term Debt Maturities [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 1,634
Long-term Debt, Current Maturities	1,634	$ 0
Long-term Debt, Maturities, Repayments of Principal in Year Two	997
Long-term Debt, Maturities, Repayments of Principal in Year Three	2,016
Long-term Debt, Maturities, Repayments of Principal in Year Four	745
Long-term Debt, Maturities, Repayments of Principal in Year Five	2,995
Long-term Debt, Maturities, Repayments of Principal after Year Five	$ 12,274

Debt - Short-term Debt (Details

Debt - Short-term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Commercial Paper	$ 0	$ 0

Debt - Line of Credit (Details)

Debt - Line of Credit (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Line of Credit Facility [Line Items]
Line Of Credit Facility Interest Rate Under Agreement Maximum	0.15%
Unsecured revolving credit agreement	$ 1,500
Debt Instrument, Unused Borrowing Capacity, Amount	2,000
Additional Credit Facility	500
Maximum Amount Of Letters Of Credit Issuable	$ 200
Line Of Credit Facility Interest Rate Under Agreement Minimum	0.05%
Facility fee (in hundredths)	0.10%
Level the debt to capitalization must be below under the facility agreement	50.00%
Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available	$ 854
Bridge Loan [Member]
Line of Credit Facility [Line Items]
Expected Proceeds From Issuance Of Long Term Debt	13,000
Term Loan [Member]
Line of Credit Facility [Line Items]
Term Loan Principal	$ 3,200

Pension and Other Postretirem79

Pension and Other Postretirement Plans Defined Benefit Plans Obligations (Details) $ in Millions		12 Months Ended
		Dec. 31, 2016USD ($)		Dec. 31, 2015USD ($)		Dec. 31, 2014USD ($)	Dec. 31, 2016USD ($)Plans		Dec. 31, 2015USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of pension plans sponsored by the company that provide benefits for our reired employees (in number of plans) | Plans							2
Voluntary contribution to the pension plan		$ 0		$ 0
Pension settlement charge	[1]	0		0		$ (112)
Minimum age of all current and future retirees and employees, who terminate employment, are eligible to participate in group health plans at their own cost. (in years of age)							55		45
Number of years service to be eligible to participate in group health plans at their own cost after retirement or termination. (in years)							5
Fair Value of Plan Assets [Roll Forward]
Actual return on plan assets		42		46
Fair value of plan assets, end of year		5,288	[2]	5,206	[3]
Funded status of pension and postretirement benefit plan [Abstract]
Fair value of plan assets		5,288	[2]	5,206	[3]		$ 5,288	[2]	$ 5,206	[3]
Defined contribution benefit savings plan [Abstract]
Pension Plan Balance To Total Benefit Obligation							96.00%
Weighted Average Discount Rate Pension Plan							4.22%		4.50%
Weighted Average Discount Rate Other postretirement plan							4.12%		4.39%
Expected Net Actuarial Losses Pension							$ 65
Expected Net Actuarial Losses Other Postretirement Plan							2
Expected amortization of prior service credits other postretirement benefits							4
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded Status of Plan							107		$ 88
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, end of year		(5,807)		(5,714)
Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, end of year		5,914		5,802
Funded status of pension and postretirement benefit plan [Abstract]
Benefit obligation		(5,807)		(5,714)			(5,807)		(5,714)
Fair value of plan assets		5,914		5,802			5,914		5,802
Non-qualified pension plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded Status of Plan							(225)		(232)
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, end of year		(225)		(232)
Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, end of year		0		0
Funded status of pension and postretirement benefit plan [Abstract]
Benefit obligation		(225)		(232)			(225)		(232)
Fair value of plan assets		0		0			0		0
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued Benefit Assets							107		88
Defined Benefit Plan, Funded Status of Plan							(118)		(144)
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Interest cost		260		261		288
Actuarial loss (gain)		161		(453)
Benefits Paid		(335)		(367)
Benefit obligation, end of year		(6,032)		(5,946)		(6,505)
Fair Value of Plan Assets [Roll Forward]
Actual return on plan assets		426		0
Employer contributions		21		22
Benefits Paid		(335)		(367)
Fair value of plan assets, end of year		5,914		5,802		6,147
Funded status of pension and postretirement benefit plan [Abstract]
Benefit obligation		(6,032)		(5,946)		(6,505)	(6,032)		(5,946)
Fair value of plan assets		5,914		5,802		6,147	5,914		5,802
Defined Benefit Plan Reconciliation Of Funded Status To Fair Value Of Assets Liabilities [Abstract]
Unrecognized prior service credit							0		(1)
Unrecognized net actuarial losses							2,460		2,398
Amount recognized in accumulated other comprehensive loss							(2,460)		(2,397)
Liabilities recognized on the balance sheet of our pension and postretirement benefit plan [Abstract]
Accrued benefit liabilities reflected in other current liabilities							(20)		(19)
Accrued benefit liabilities reflected in other long-term liabilities							(205)		(213)
Pension and Other Postretirement Defined Benefit Plans, Liabilities							118		144
Defined contribution benefit savings plan [Abstract]
Unrecognized net actuarial losses							2,460		2,398
Unrecognized prior service credit							0		(1)
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued Benefit Assets							0		0
Defined Benefit Plan, Funded Status of Plan							(196)		(202)
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Interest cost		11		11		12
Actuarial loss (gain)		0		(10)
Benefits Paid		(20)		(21)
Benefit obligation, end of year		(248)		(257)		(277)
Fair Value of Plan Assets [Roll Forward]
Actual return on plan assets		1		1
Employer contributions		16		17
Benefits Paid		(20)		(21)
Fair value of plan assets, end of year		52		55		58
Funded status of pension and postretirement benefit plan [Abstract]
Benefit obligation		(248)		(257)		(277)	(248)		(257)
Fair value of plan assets		$ 52		$ 55		$ 58	52		55
Defined Benefit Plan Reconciliation Of Funded Status To Fair Value Of Assets Liabilities [Abstract]
Unrecognized prior service credit							(19)		(22)
Unrecognized net actuarial losses							66		67
Amount recognized in accumulated other comprehensive loss							(47)		(45)
Liabilities recognized on the balance sheet of our pension and postretirement benefit plan [Abstract]
Accrued benefit liabilities reflected in other current liabilities							(13)		(14)
Accrued benefit liabilities reflected in other long-term liabilities							(183)		(188)
Pension and Other Postretirement Defined Benefit Plans, Liabilities							196		202
Defined contribution benefit savings plan [Abstract]
Unrecognized net actuarial losses							66		67
Unrecognized prior service credit							$ (19)		$ (22)
Lump-sum distribution percentage [Member] | Pension Settlement Charge [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension Lump Sum Percentage				100.00%
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
[2]	Excludes $180 million of cash and cash equivalents and other payables.
[3]	Excludes $133 million of cash and cash equivalents and other payables.

Pension and Other Postretirem80

Pension and Other Postretirement Plans Defined Benefit Plans Periodic Benefit (Income) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Component Abstract
Pension settlement charge	[1]	$ 0	$ 0	$ (112)
Assumed healthcare cost trend rates for medical and prescription drug costs [Abstract]
Medical cost trend rate for the next fiscal year (Defined Benefit Plans) (in hundredths)		5.50%
Ultimate future medical cost trend rate beyond next fiscal year to 2023 (Defined Benefit Plans) (in hundredths)		4.50%
Prescription drug cost trend rate for the next fiscal year (Defined Benefit Plans) (in hundredths)		10.20%
Ultimate future prescription drug cost trend rate beyond next fiscal year to 2023 (Defined Benefit Plans) (in hundredths)		4.50%
Employer voluntary contributions in next fiscal year		$ 60
Pension Plan [Member]
Operating Component Abstract
Amortization of prior service cost		0	(1)	(1)
Financing Component Abstract
Interest cost		260	261	288
Expected return on plan assets		(389)	(419)	(422)
Recognized net actuarial losses		61	62	47
Net periodic benefit cost (income)		(68)	(97)	$ 24
Defined Benefit Plan, Plan Amendment [Abstract]
Employer Contributions		$ 21	$ 22
Weighted average assumptions used to determine net periodic benefit cost (income) [Abstract]
Discount rate (in hundredths)		4.50%	4.12%	4.96%
Expected long-term return on plan assets (in hundredths)		6.90%	7.00%	7.00%
OPEB Plans [Member]
Operating Component Abstract
Amortization of prior service cost		$ (4)	$ (4)	$ (4)
Financing Component Abstract
Interest cost		11	11	12
Expected return on plan assets		(3)	(3)	(3)
Recognized net actuarial losses		3	3	1
Net periodic benefit cost (income)		7	7	$ 6
Defined Benefit Plan, Plan Amendment [Abstract]
Employer Contributions		$ 16	$ 17
Weighted average assumptions used to determine net periodic benefit cost (income) [Abstract]
Discount rate (in hundredths)		4.39%	4.02%	4.73%
Expected long-term return on plan assets (in hundredths)		4.75%	5.30%	5.30%
Assumed healthcare cost trend rates for medical and prescription drug costs [Abstract]
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components		$ 0.3
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation		8
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components		0.2
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation		7
Pension Settlement Charge [Member] | Pension Plan [Member]
Financing Component Abstract
Pension settlement charge		0	$ 0	$ 112
Pension Settlement Charge [Member] | OPEB Plans [Member]
Financing Component Abstract
Pension settlement charge		$ 0	$ 0	$ 0
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.

Pension and Other Postretirem81

Pension and Other Postretirement Plans Defined Benefit Plans Expected Benefit (Details) $ in Millions	Dec. 31, 2016USD ($)
Defined Benefit Plan Disclosure [Line Items]
Expected Net Actuarial Losses Pension	$ 65
Expected Net Actuarial Losses Other Postretirement Plan	2
Expected amortization of prior service credits other postretirement benefits	4
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
2,016	495
2,017	360
2,018	360
2,019	362
2,020	366
2021-2025	1,844
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2,016	18
2,017	18
2,018	18
2,019	18
2,020	17
2021-2025	$ 82

Pension and Other Postretirem82

Pension and Other Postretirement Plans Assets of the Aetna Pension Plan Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	$ 5,288	[1]	$ 5,206	[2]
Cash And Cash Equivalents And Other Payables Excluded From Total Investments Of The Pension Plan Assets	180		133
Pension Plan [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	5,914		5,802		$ 6,147
Pension Plan [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	2,410	[1]	2,225	[2]
Pension Plan [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	2,400	[1]	2,481	[2]
Pension Plan [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	478	[1]	500	[2]
Pension Plan [Member] | Debt Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	2,390		2,351
Pension Plan [Member] | Debt Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	460		428
Pension Plan [Member] | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	1,930		1,920
Pension Plan [Member] | Debt Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		3
Pension Plan [Member] | Equity Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	1,955		1,802
Pension Plan [Member] | Equity Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	1,950		1,797
Pension Plan [Member] | Equity Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	5		5
Pension Plan [Member] | Equity Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Real Estate [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	478		497
Pension Plan [Member] | Real Estate [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Real Estate [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Real Estate [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	478		497
Pension Plan [Member] | Other Investments [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	943		1,053
Pension Plan [Member] | Other Investments [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Other Investments [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	465		556
Pension Plan [Member] | Other Investments [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	478		497
Pension Plan [Member] | US Treasury and Government [Member] | Debt Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	582		563
Pension Plan [Member] | US Treasury and Government [Member] | Debt Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	460		428
Pension Plan [Member] | US Treasury and Government [Member] | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	122		135
Pension Plan [Member] | US Treasury and Government [Member] | Debt Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | States, municipalities and political subdivisions [Member] | Debt Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	128		126
Pension Plan [Member] | States, municipalities and political subdivisions [Member] | Debt Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | States, municipalities and political subdivisions [Member] | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	128		126
Pension Plan [Member] | States, municipalities and political subdivisions [Member] | Debt Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | U.S. corporate securities [Member] | Debt Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	1,291		1,231
Pension Plan [Member] | U.S. corporate securities [Member] | Debt Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | U.S. corporate securities [Member] | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	1,291		1,229
Pension Plan [Member] | U.S. corporate securities [Member] | Debt Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		2
Pension Plan [Member] | Foreign securities [Member] | Debt Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	103		136
Pension Plan [Member] | Foreign securities [Member] | Debt Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Foreign securities [Member] | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	103		136
Pension Plan [Member] | Foreign securities [Member] | Debt Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Residential mortgage-backed securities [Member] | Debt Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	163		196
Pension Plan [Member] | Residential mortgage-backed securities [Member] | Debt Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Residential mortgage-backed securities [Member] | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	163		196
Pension Plan [Member] | Residential mortgage-backed securities [Member] | Debt Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Commercial mortgage-backed securities [Member] | Debt Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	57		52
Pension Plan [Member] | Commercial mortgage-backed securities [Member] | Debt Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Commercial mortgage-backed securities [Member] | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	57		51
Pension Plan [Member] | Commercial mortgage-backed securities [Member] | Debt Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		1
Pension Plan [Member] | Other asset-backed securities [Member] | Debt Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	60		40
Pension Plan [Member] | Other asset-backed securities [Member] | Debt Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Other asset-backed securities [Member] | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	60		40
Pension Plan [Member] | Other asset-backed securities [Member] | Debt Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Redeemable Preferred Securities [Member] | Debt Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	6		7
Pension Plan [Member] | Redeemable Preferred Securities [Member] | Debt Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Redeemable Preferred Securities [Member] | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	6		7
Pension Plan [Member] | Redeemable Preferred Securities [Member] | Debt Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | US Domestic securities [Member] | Equity Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	1,310		1,227
Pension Plan [Member] | US Domestic securities [Member] | Equity Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	1,305		1,222
Pension Plan [Member] | US Domestic securities [Member] | Equity Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	5		5
Pension Plan [Member] | US Domestic securities [Member] | Equity Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | International [Member] | Equity Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	611		547
Pension Plan [Member] | International [Member] | Equity Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	611		547
Pension Plan [Member] | International [Member] | Equity Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | International [Member] | Equity Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Common/collective trusts | Debt Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	158		254
Pension Plan [Member] | Common/collective trusts | Equity Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	307		302
Pension Plan [Member] | Common/collective trusts | Other Investments [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	465	[3]	556	[4]
Pension Plan [Member] | Common/collective trusts | Other Investments [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0	[3]	0	[4]
Pension Plan [Member] | Common/collective trusts | Other Investments [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	465	[3]	556	[4]
Pension Plan [Member] | Common/collective trusts | Other Investments [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0	[3]	0	[4]
Pension Plan [Member] | Domestic Real Estate [Member] | Equity Securities [Member]
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	34		28
Pension Plan [Member] | Domestic Real Estate [Member] | Equity Securities [Member] | Level 1
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	34		28
Pension Plan [Member] | Domestic Real Estate [Member] | Equity Securities [Member] | Level 2
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	0		0
Pension Plan [Member] | Domestic Real Estate [Member] | Equity Securities [Member] | Level 3
Assets of the Aetna Pension Plan Fair Value [Line Items]
Fair value of plan assets	$ 0		$ 0
[1]	Excludes $180 million of cash and cash equivalents and other payables.
[2]	Excludes $133 million of cash and cash equivalents and other payables.
[3]	The assets in the underlying funds of common/collective trusts are comprised of $307 million of equity securities and $158 million of debt securities.
[4]	The assets in the underlying funds of common/collective trusts are comprised of $302 million of equity securities and $254 million of debt securities.

Pension and Other Postretirem83

Pension and Other Postretirement Plans Assets of the Aetna Pension Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Reconciliation Of Level 3 Plan Assets [Roll Forward]
Beginning balance	$ 500	$ 472
Actual return on plan assets	42	46
Purchases, sales and settlements	(62)	(19)
Transfers Out Of Level 3	(2)	1
Ending balance	478	500	$ 472
Pension Plan [Member]
Defined Benefit Plan Reconciliation Of Level 3 Plan Assets [Roll Forward]
Actual return on plan assets	$ 426	$ 0
Expected Return On Plan Assets [Abstract]
Expected long-term return on plan assets (in hundredths)	6.90%	7.00%	7.00%
OPEB Plans [Member]
Defined Benefit Plan Reconciliation Of Level 3 Plan Assets [Roll Forward]
Actual return on plan assets	$ 1	$ 1
Expected Return On Plan Assets [Abstract]
Defined Benefit Plan, Expected Percentage Return on Plan Assets	4.75%	5.30%	5.30%
Expected long-term return on plan assets (in hundredths)	4.75%	5.30%	5.30%
Debt Securities [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	48.00%
Debt Securities [Member] | OPEB Plans [Member]
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Actual Allocation percentage (in hundredths)	82.00%	83.00%
Minimum target allocation (in hundredths)	80.00%	80.00%
Maximum target allocation (in hundredths)	90.00%	90.00%
Real Estate Investment [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	7.00%
Real Estate Investment [Member] | OPEB Plans [Member]
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Actual Allocation percentage (in hundredths)	7.00%	7.00%
Minimum target allocation (in hundredths)	0.00%	0.00%
Maximum target allocation (in hundredths)	10.00%	10.00%
Private Equity Funds [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	4.00%
Equity Securities [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	38.00%
Equity Securities [Member] | OPEB Plans [Member]
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Actual Allocation percentage (in hundredths)	11.00%	10.00%
Minimum target allocation (in hundredths)	5.00%	5.00%
Maximum target allocation (in hundredths)	15.00%	15.00%
Real Estate [Member] | Pension Plan [Member]
Defined Benefit Plan Reconciliation Of Level 3 Plan Assets [Roll Forward]
Beginning balance	$ 497	$ 470
Actual return on plan assets	42	46
Purchases, sales and settlements	(61)	(19)
Transfers Out Of Level 3	0	0
Ending balance	478	497	$ 470
Other Assets [Member] | Pension Plan [Member]
Defined Benefit Plan Reconciliation Of Level 3 Plan Assets [Roll Forward]
Beginning balance	3	2
Actual return on plan assets	0	0
Purchases, sales and settlements	(1)	0
Transfers Out Of Level 3	(2)	1
Ending balance	$ 0	$ 3	$ 2
Hedge Funds [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	3.00%
Minimum [Member] | Debt Securities [Member] | OPEB Plans [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	80.00%	80.00%
Minimum [Member] | Equity Securities [Member] | OPEB Plans [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	5.00%	5.00%
Minimum [Member] | Other Securities [Member] | OPEB Plans [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	0.00%	0.00%
Maximum [Member] | Debt Securities [Member] | OPEB Plans [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	90.00%	90.00%
Maximum [Member] | Equity Securities [Member] | OPEB Plans [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	15.00%	15.00%
Maximum [Member] | Other Securities [Member] | OPEB Plans [Member]
Assets of the Aetna Pension Plan [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations	10.00%	10.00%

Pension and Other Postretirem84

Pension and Other Postretirement Plans 401(k) Plan (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employer match percentage on annual eligible employee earnings (in hundredths)	100.00%
Defined Contribution Pension And Other Postretirement Plans Employee Deferral Percentage Maximum Eligible For Employer Match	6.00%
Emplyer matching contributions during the period	$ 197	$ 198	$ 180
Number of shares of common stock held by the plan trustee for plan participants (in shares)	7
Approximate number of shares of common stock reserved for issuance under the 401(k) plan (in shares)	34

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Current taxes: [Abstract]
Federal									$ 1,662		$ 1,797		$ 1,233
State									129		112		84
Total current taxes									1,791		1,909		1,317
Deferred taxes (benefits): [Abstract]
Federal									(55)		(59)		114
State									(1)		(9)		24
Total deferred income taxes									(56)		(68)		138
Income taxes	$ 147	$ 476	$ 561	$ 551	$ 263	$ 461	$ 527	$ 590	1,735	[1]	1,841	[1]	1,455	[1]
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Application of the tax rate									1,397		1,483		1,225
Health insurer fee									293		300		212
State income taxes									83		63		78
Other, net									(38)		(5)		(60)
Income taxes	147	$ 476	$ 561	$ 551	263	$ 461	$ 527	$ 590	$ 1,735	[1]	$ 1,841	[1]	$ 1,455	[1]
Tax rate									35.00%		35.00%		35.00%
Health Insurer Fee Tax Effect, Percent									7.30%		7.10%		6.10%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent									2.10%		1.50%		2.20%
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent									(0.90%)		(0.10%)		(1.70%)
Effective Income Tax Rate Reconciliation, Percent									43.50%		43.50%		41.60%
Deferred tax assets: [Abstract]
Insurance reserves	231				302				$ 231		$ 302
Reserve for anticipated future losses on discontinued products	225				268				225		268
Employee and postretirement benefits	196				220				196		220
Net operating losses	147				165				147		165
Severance and facilities	135				18				135		18
Investments, net	80				92				80		92
Debt fair value adjustment	23				33				23		33
Deferred revenue	21				21				21		21
Other	117				66				117		66
Gross deferred tax assets	1,175				1,185				1,175		1,185
Less: Valuation allowance	118				128				118		128
Deferred tax assets, net of valuation allowance	1,057				1,057				1,057		1,057
Deferred tax liabilities: [Abstract]
Goodwill and other acquired intangible assets	814				863				814		863
Cumulative depreciation and amortization	185				231				185		231
Unrealized gains on investment securities	42				138				42		138
Other	20				2				20		2
Total gross deferred tax liabilities	1,061				1,234				1,061		1,234
Net deferred tax assets	$ (4)				$ (177)				$ (4)		$ (177)
[1]	Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer.

Stock-based Employee Incentiv86

Stock-based Employee Incentive Plans (Details)		12 Months Ended
		Dec. 31, 2016USD ($)sharesyears$ / shares		Dec. 31, 2015USD ($)years$ / sharesshares		Dec. 31, 2014USD ($)years$ / sharesshares		Dec. 31, 2013USD ($)years$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		23,000,000
Maximum vesting percentage for stock options and stock appreciation rights (in hundredths)		100.00%
Stock Appreciation Rights Vesting Period		3
Assumptions used to calculate the weighted-average fair value of options and SARs [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term		7 years 40 days		6 years 176 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate		32.90%		33.40%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate		1.52%		1.81%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate		0.91%		1.13%
Share Price | $ / shares		$ 103.45		$ 100.50
PSAR Minimum Vesting Amount		0
PSAR Maximum Vesting Amount		700,000
Amount of PSARs Vested		500,000
Assumptions used to calculate grant date fair value of PSARs [Abstract]
Weighted-average per share value (PSARs) | $ / shares						$ 18.64
Dividend yield PSARs (in hundredths)						1.25%
Expected settlement period for PSARs						6 years 44 days
Historical Volatility PSARs (in hundredths)						40.40%
Risk Free Interest Rates PSARs (in hundredths)						0.60%
Initial Price PSARs | $						$ 64.25
Outstanding, beginning of year		7,400,000	[1]	8,100,000	[1]	10,500,000
Granted		2,400,000		2,000,000		1,400,000
Exercised		1,400,000		2,500,000		3,700,000
Expired or forfeited		400,000		200,000		100,000
Outstanding, end of year		8,000,000		7,400,000	[1]	8,100,000	[1]	10,500,000
Exercisable, end of year		4,300,000		4,100,000		6,100,000
Number Of Stock Options And Stock Appreciation Rights [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price | $ / shares		$ 57.26		$ 45.88		$ 42.86
WeightedAverageExercisePrice [Abstract]
Stock options and stock appreciation rights outstanding at beginning of year weighted average exercise price (in dollars per share) | $ / shares		64.11	[1]	49.37	[1]	43.27
Stock options and stock appreciation rights granted weighted average exercise price (in dollars per share) | $ / shares		104.47		101.41		72.36
Stock options and stock appreciation rights exercised weighted average exercise price (in dollars per share) | $ / shares		52.99		43.90		40.50
Stock options and stock appreciation rights forfeited weighted average exercise price (in dollars per share) | $ / shares		83.25		91.25		46.94
Stock options and stock appreciation rights outstanding at end of period weighted average exercise price (in dollars per share) | $ / shares		$ 77.20		$ 64.11	[1]	$ 49.37	[1]	$ 43.27
Weighted Average Remaining Contractual Life [Abstract]
Stock options and stock appreciation rights outstanding at beginning of year weighted average remaining contractual life (in years) | years		5.3	[1]	4.2	[1]	3.5
Stock options and stock appreciation rights outstanding at end of period weighted average remaining contractual life (in years) | years		5.9		5.3	[1]	4.2	[1]	3.5
Stock options and stock appreciation rights exercisable at end of year weighted average remaining contractual life (in years) | years		3.6		2.6		2.6
Aggregate Intrinsic Value [Abstract]
Stock options and stock appreciation rights outstanding at beginning of year aggregate intrinsic value | $		$ 325,000,000	[1]	$ 318,000,000	[1]	$ 265,000,000
Stock options and stock appreciation rights exercised aggregate intrinsic value | $		85,000,000		155,000,000		132,000,000
Stock options and stock appreciation rights outstanding at end of period aggregate intrinsic value | $		373,000,000		325,000,000	[1]	318,000,000	[1]	$ 265,000,000
Stock options and stock appreciation rights exercisable at end of year aggregate intrinsic value (in dollars per share) | $		287,000,000		252,000,000		280,000,000
Activity under various plans [Abstract]
Cash received from stock option exercises | $		0		7,000,000		32,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $		384,000,000		413,000,000		323,000,000
Tax benefits realized for the tax deductions from stock options and stock appreciation rights | $		77,000,000		101,000,000		87,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value | $	[2]	$ 223,000,000		$ 126,000,000		$ 107,000,000
Number Of Shares Common Stock Received For Each Stock Unit Granted		1
Maximum vesting percentage for restricted stock units (in hundredths)		100.00%
Market Stock Unit Vesting Period		3
Vesting Percentage For Market Stock Units Range Minimum		0.00%
Vesting Percentage For Market Stock Units Range Maximum		150.00%
Minimum Vesting Percentage During Performance Period For Performance Stock Units		0.00%
Maximum Vesting Percentage During Performance Period For Performance Stock Units		200.00%
Performance Stock Unit Vesting Period		3		3		3		2
Assumptions used to calculate the weighted-average fair value of options for market stock units [Abstract]
Dividend yield market stock units (in hundredths)						1.30%
Historical volatility market stock units (in hundredths)						26.40%
Risk-free interest rates market stock units (in hundredths)						0.70%
Initial Price for market stock units | $						$ 72.26
Summary of the status of restricted stock units, market stock units, and performance stock units [Roll Forward]
Outstanding restricted stock units, market stock units, and performance stock units at beginning of year (in shares)		3,900,000		5,100,000		5,300,000
Restricted stock units, market stock units, and performance stock units during period - Granted (in shares)		2,100,000		1,800,000		2,700,000
Restricted stock units, market stock units, and performance stock units - Vested (in shares)		(2,700,000)		(2,600,000)		(2,500,000)
Restricted stock units, market stock units, and performance stock units - Forfeited (in shares)		(400,000)		(400,000)		(400,000)
Outstanding restricted stock units, market stock units and performance stock units at end of year (in shares)		2,900,000		3,900,000		5,100,000		5,300,000
Outstanding restricted stock units, market stock units, and performance stock units at beginning of year - weighted-average grant date fair value (in dollars per share) | $ / shares		$ 73.40		$ 58.57		$ 48.82
Restricted stock units, market stock units, and performance stock units - weighted-average grant date fair value - Granted (in dollars per share) | $ / shares		98.60		100.52		71.88
Restricted stock units, market stock units, and performance stock units - weighted-average grant date fair value - Vested (in dollars per share) | $ / shares		68.87		59.72		50.11
Restricted stock units, market stock units, and performance stock units - weighted-average grant date fair value - Forfeited (in dollars per share) | $ / shares		71.17		70.94		56.89
Outstanding stock performance units and restricted stock units at end of year - weighted-average grant date fair value (in dollars per share) | $ / shares		$ 91.95		$ 73.40		$ 58.57		$ 48.82
Pretax share-based compensation expense in general and administrative expenses recorded | $		$ 191,000,000		$ 181,000,000		$ 163,000,000
Related tax benefits recorded | $		33,000,000		$ 37,000,000		$ 37,000,000
Total unrecognized compensation costs related to stock options, stock appreciation rights, restricted stock units, market stock units and performance stock units | $		$ 185,000,000
Weighted-average period unrecognized compensation costs related to stock options, stock appreciation rights, restricted stock units, market stock units and performance stock units is expected to be recognized (in years)		1 year 238 days
Price Range $20.00-$30.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options	[3]	0
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term (in years) | years	[3]	2.4
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price, End of Period (in dollars per share) | $ / shares	[3]	$ 24.97
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $	[3]	$ 2,000,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Number Of Outstanding Options	[3]	0
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Weighted-Average Price | $ / shares	[3]	$ 24.97
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Aggregate Intrinsic Value | $	[3]	$ 2,000,000
Price Range $30.00-$40.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		1,100,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term (in years) | years		2.1
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price, End of Period (in dollars per share) | $ / shares		$ 32.11
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $		$ 98,000,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Number Of Outstanding Options		1,100,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Weighted-Average Price | $ / shares		$ 32.11
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Aggregate Intrinsic Value | $		$ 98,000,000
Price Range $40.00-$50.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		700,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term (in years) | years		0.4
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price, End of Period (in dollars per share) | $ / shares		$ 45.55
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $		$ 53,000,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Number Of Outstanding Options		700,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Weighted-Average Price | $ / shares		$ 45.55
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Aggregate Intrinsic Value | $		$ 53,000,000
Price Range $50.00-$60.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		800,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term (in years) | years		1.1
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price, End of Period (in dollars per share) | $ / shares		$ 50.70
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $		$ 59,000,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Number Of Outstanding Options		800,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Weighted-Average Price | $ / shares		$ 50.70
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Aggregate Intrinsic Value | $		$ 59,000,000
Price Range $60.00-$70.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		500,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term (in years) | years		6.6
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price, End of Period (in dollars per share) | $ / shares		$ 64.25
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $		$ 30,000,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Number Of Outstanding Options		500,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Weighted-Average Price | $ / shares		$ 64.25
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Aggregate Intrinsic Value | $		$ 30,000,000
Price Range $70.00-$80.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		1,000,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term (in years) | years		6.8
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price, End of Period (in dollars per share) | $ / shares		$ 72.34
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $		$ 50,000,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Number Of Outstanding Options	[3]	600,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Weighted-Average Price | $ / shares		$ 72.34
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Aggregate Intrinsic Value | $		$ 31,000,000
Price Range $80.00-$100.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		0
Price Range $100.00-$110.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		3,600,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term (in years) | years		8.6
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price, End of Period (in dollars per share) | $ / shares		$ 102.36
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $		$ 79,000,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Number Of Outstanding Options	[3]	600,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Weighted-Average Price | $ / shares		$ 101.05
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Aggregate Intrinsic Value | $		$ 14,000,000
Price Range $110.00-$120.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		300,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term (in years) | years		9.2
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price, End of Period (in dollars per share) | $ / shares		$ 115.29
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $		$ 2,000,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Number Of Outstanding Options	[3]	0
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Weighted-Average Price | $ / shares		$ 0
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Aggregate Intrinsic Value | $		$ 0
Price Range $120.00-$130.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		0
Total $20.00 - $130.00
Aggregate Intrinsic Value [Abstract]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options	[4]	8,000,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term (in years) | years	[4]	5.9
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price, End of Period (in dollars per share) | $ / shares	[4]	$ 77.20
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $	[4]	$ 373,000,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Number Of Outstanding Options	[4]	4,300,000
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Weighted-Average Price | $ / shares	[4]	$ 57.26
Share Based Compensation Shares Exercisable Under Stock Options And Stock Appreciation Rights Plans Exercise Price Range Aggregate Intrinsic Value | $	[4]	$ 287,000,000
Two year vesting period [Member]
Activity under various plans [Abstract]
Market Stock Unit Vesting Period				two
Three year vesting period [Member]
Activity under various plans [Abstract]
Weighted average per share fair value of market stock units granted (in dollars per share) | $ / shares						$ 74.99
Stock Appreciation Rights (SARs) [Member]
Assumptions used to calculate the weighted-average fair value of options and SARs [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares		$ 34.33		$ 32.13
PSUs granted in 2013
Activity under various plans [Abstract]
Percentage of original number of performance stock units original granted in period which vested in period				74.61%		131.62%		127.08%
PSUs granted in 2014 [Member]
Activity under various plans [Abstract]
Percentage of original number of performance stock units original granted in period which vested in period		200.00%
[1]	PSARs are included in this table in 2015 and 2014 at the maximum amount that could potentially vest
[2]	The fair value represents the aggregate grant date fair value of the stock options, SARs, PSARs and stock units as of the respective grant dates.
[3]	The number of outstanding and exercisable SARs and PSARs with exercise prices between $20 and $30 rounded to zero.
[4]	The number of outstanding SARs with exercise prices between $80 and $100 and between $120 and $130 rounded to zero.

Shareholders' Equity - Repurcha

Shareholders' Equity - Repurchases (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 17, 2017	Dec. 31, 2013
Equity, Class of Treasury Stock [Line Items]
Amount of repurchases under the program		$ 296	$ 1,218
Repurchase authorizations remaining at period end	$ 1,083	$ 1,083	1,379
July Accelerated Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Number of shares purchased (in shares)		0.9
Accelerated Share Repurchases, Settlement (Payment) or Receipt		$ 100
Authorization Date November 2014 [Member]
Equity, Class of Treasury Stock [Line Items]
Purchases not to exceed			$ 1,000
Number of shares purchased (in shares)	0	0	0
Amount of repurchases under the program	$ 0	$ 0	$ 0
Authorization Date February 2014 [Member]
Equity, Class of Treasury Stock [Line Items]
Purchases not to exceed			$ 1,000
Number of shares purchased (in shares)	0	3	7.6
Amount of repurchases under the program	$ 0	$ 296	$ 621
Authorization Date September 2013 [Member]
Equity, Class of Treasury Stock [Line Items]
Purchases not to exceed					$ 750
Number of shares purchased (in shares)	0	0	8.3
Amount of repurchases under the program	$ 0	$ 0	$ 597
Total Repurchases [Member]
Equity, Class of Treasury Stock [Line Items]
Number of shares purchased (in shares)	0	3	15.9
Amount of repurchases under the program	$ 0	$ 296	$ 1,218
Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Purchases not to exceed				$ 4,000

Shareholders' Equity - Dividend

Shareholders' Equity - Dividends (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Feb. 17, 2017
Dividends Payable [Line Items]
Total Dividends	$ 88,000,000	$ 88,000,000	$ 88,000,000	$ 88,000,000	$ 87,000,000	$ 87,000,000	$ 87,000,000	$ 87,000,000
Dividends Amount Per Share	$ 0.250	$ 0.250	$ 0.250	$ 0.250	$ 0.250	$ 0.250	$ 0.250	$ 0.250	$ 0.250
Maximum Value of Dividends Declared									$ 0.25
Subsequent Event [Member]
Dividends Payable [Line Items]
Dividends Amount Per Share										$ 0.500

Shareholders' Equity - Stock Un

Shareholders' Equity - Stock Units (Details) shares in Millions	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Class of Stock [Line Items]
Number Of Undesignated Shares Available (in shares)	442
Preferred Class A [Member]
Class of Stock [Line Items]
Number of authorized Class A voting preferred stock (in shares)	8
Number of authorized Class A voting preferred stock, par value per share (in dollars per shares) | $ / shares	$ 0.01

Shareholders' Equity Statutory

Shareholders' Equity Statutory Accounting Practices (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shareholders' Equity - Statutory Accounting Practices [Abstract]
Statutory Accounting Practices, Statutory Net Income Amount	$ 2,229	$ 2,186	$ 2,127
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	10,413	$ 9,883	$ 9,406
Proceeds From Insurance And Health Maintenance Organizations	2,300
Statutory Accounting Practices, Statutory Capital and Surplus Required	3,738
Assets Held by Insurance Regulators	561
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval	$ 1,902

Other Comprehensive (Loss) In91

Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period		$ (1,330)
Other Comprehensive Income (Loss)		(222)	$ (219)	$ (199)
Balance at end of period		(1,552)	(1,330)
Pension settlement charge	[1]	0	0	112
Net Unrealized Gains (Losses) Previously Impaired Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	[2]	19	35	34
Balance at end of period	[2]	16	19	35
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	[2]	(20)	(45)	1
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	[2]	(31)	(69)	1
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	[2],[3]	(17)	(29)	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	[2],[3]	(26)	(44)	0
Net Unrealized Gains (Losses) All Other Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period		312	568	327
Balance at end of period		297	312	568
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		(8)	(318)	237
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax		(12)	(490)	365
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	[3]	7	(62)	(4)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	[3]	11	(97)	(7)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period		(74)	(61)	0
Balance at end of period		(235)	(74)	(61)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax		(177)	(17)	(58)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss), before Reclassification and Tax		(273)	(26)	(90)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	[4]	(16)	(4)	3
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax	[4]	(25)	(6)	4
Pension and OPEB Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period		(1,587)	(1,653)	(1,273)
Balance at end of period		(1,630)	(1,587)	(1,653)
Other comprehensive income, Pensions and Other Post Retirement Employee Benefit Plans, net of tax		(82)	27	(481)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax		(126)	41	(739)
Defined Benefit Plan Recognized Net Gain (Loss) Due to Settlements, Net of Tax	[5]	0	0	73
Pension settlement charge	[5]			112
Recognized net actuarial losses	[5]	(42)	(42)	(31)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	[5]	(64)	(64)	(48)
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Net of Tax	[5]	3	3	3
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	[5]	5	4	4
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period		(1,330)	(1,111)	(912)
Balance at end of period		(1,552)	(1,330)	(1,111)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other Comprehensive Income (Loss)		(161)	(13)	(61)
Net Unrealized Gains (Losses) All Other Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other Comprehensive Income (Loss)		(15)	(256)	241
Net Unrealized Gains (Losses) Previously Impaired Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other Comprehensive Income (Loss)	[2]	(3)	(16)	1
Pension and OPEB Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other Comprehensive Income (Loss)		$ (43)	$ 66	$ (380)
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
[2]	Represents specifically identified unrealized gains on the non-credit related component of impaired debt securities that we do not intend to sell and subsequent changes in the fair value of any previously impaired security.
[3]	Reclassifications out of accumulated other comprehensive income for specifically identified previously impaired debt securities and all other securities are reflected in net realized capital gains (losses) within the Consolidated Statements of Income.
[4]	Reclassifications out of accumulated other comprehensive income for specifically identified foreign currency gains (losses) and derivatives are reflected in net realized capital gains (losses) within the Consolidated Statements of Income, except for the specifically identified effective portion of derivatives related to interest rate swaps which are reflected in interest expense. Refer to Note 9 for additional information.
[5]	Reclassifications out of accumulated other comprehensive income for specifically identified pension and OPEB plan expenses are reflected in general and administrative expenses within the Consolidated Statements of Income. During 2014, our reclassifications out of accumulated other comprehensive income for the Aetna Pension Plan reflect a pension settlement charge of $73 million ($112 million pretax). (Refer to Note 10 for additional information).

Earnings Per Common Share (Deta

Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended																12 Months Ended
		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Earnings Per Share, Basic and Diluted [Line Items]
Net income attributable to the Aetna		$ 139		$ 604		$ 791		$ 737		$ 321		$ 560		$ 732		$ 777		$ 2,271	[1]	$ 2,390	[1]	$ 2,041	[1]
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average shares used to compute basic EPS (in shares)																		351.3		349.3		355.5
Dilutive effect of outstanding stock-based compensation awards (in shares)																		3		3.3		3.6
Weighted average shares used to compute diluted EPS (in shares)																		354.3		352.6		359.1
Basic EPS (in dollars per share)		$ 0.40	[2]	$ 1.72	[2]	$ 2.25	[2]	$ 2.10	[2]	$ 0.92	[2]	$ 1.60	[2]	$ 2.10	[2]	$ 2.22	[2]	$ 6.46		$ 6.84		$ 5.74
Diluted EPS (in dollars per share)		$ 0.39	[2]	$ 1.70	[2]	$ 2.23	[2]	$ 2.09	[2]	$ 0.91	[2]	$ 1.59	[2]	$ 2.08	[2]	$ 2.20	[2]	$ 6.41		$ 6.78		$ 5.68
Stock Appreciation Rights (SARs) [Member]
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	[3]																	0.1		0.5		0.3
Equity Award
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	[4]																	0.7		0.8		1.2
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
[2]	Calculation of net income attributable to Aetna per share is based on weighted average shares outstanding during each quarter and, accordingly, the sum may not equal the total for the year.
[3]	SARs are excluded from the calculation of diluted EPS if the exercise price is greater than the average market price of Aetna common shares during the period (i.e., the awards are anti-dilutive).
[4]	Performance stock units ("PSUs"), certain market stock units ("MSUs") with performance conditions, and performance stock appreciation rights ("PSARs") are excluded from the calculation of diluted EPS if all necessary performance conditions have not been satisfied at the end of the reporting period (refer to Note 12 for additional information about PSARs).

Reinsurance (Details)

Reinsurance (Details) $ in Millions		12 Months Ended
		Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Total reinsurance recoverables		$ 1,019	$ 1,214
Three Years Reinsurance Agreement With Unrelated Insurer		3
Five Years Reinsurance Agreement With Unrelated Insurer		5
Number of Reinsurance Contracts Entered Into		2
Four Years Reinsurance Agreement With Unrelated Insurer		4
Direct Premiums Earned		$ 54,062	51,539	$ 49,497
Assumed Premiums Earned		402	368	316
Ceded Premiums Earned		(348)	(289)	(251)
Health care premiums		54,116	51,618	49,562
Policyholder Benefits and Claims Incurred, Direct		44,341	42,038	40,980
Policyholder Benefits and Claims Incurred, Assumed		339	298	263
Policyholder Benefits and Claims Incurred, Ceded		(425)	(624)	(496)
Health care costs	[1]	44,255	41,712	$ 40,747
Other Reinsurance Entities [Member]
Total reinsurance recoverables		164	138
Reinsurance Entity 3 [Member]
Total reinsurance recoverables		202	395
Reinsurance Entity 2 [Member]
Total reinsurance recoverables		209	223
Reinsurance Entity 1 [Member]
Total reinsurance recoverables		$ 444	$ 458
[1]	Health care costs have been reduced by Insured member co-payments related to our mail order and specialty pharmacy operations of $115 million, $117 million and $107 million for 2016, 2015 and 2014, respectively.

Commitments and Contingencies94

Commitments and Contingencies (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Long-term Debt		$ 20,661	$ 7,787
Aggregate maximum exposures under Administrative Services Contracts to banks for funding claims paid to customers		250
Contractual obligations to maintain the required level of separate account assets for specific pensions annuities		1,800	2,000
Supplier agreement, minimum volume commitment		24
Loss Contingency, Discounted Amount of Insurance-related Assessment Liability		$ 230
Loss on Contract Termination, Percent of Total Costs		70.00%
Loss on Redemption of Notes		$ 420
Debt Instrument Redemption, Premium		100
Litigation Settlement, Expense						$ 120
Settlement of class action litigation, after-tax						$ 78
Release of litigation-related reserve, pre-tax	[1]	0	0	$ 103
Charges for changes in our life claim payments practices, net of tax					$ 36
Charge for changes in our life claim payment practices					$ 55
Rental expenses for operating leases of office space and certain computer and other equipment		167	$ 165	$ 177
Operating Leases, Future Minimum Payments Due [Abstract]
2,017		143
2,018		121
2,019		81
2,020		47
2,021		37
Funding Requirements For Partnerhips Investments And Commercial Mortgage Loans [Abstract]
2,017		177
2,018		127
2,019		94
2,020		56
2,021		37
Total Funding Requirements [Abstract]
2,017		320
2,018		248
2,019		175
2,020		103
2,021		74
Debt Issued for Humana Acquisition [Domain]
Debt Instrument, Face Amount		13,000
Long-term Debt		$ 10,200
Debt Instrument, Redemption Price, Percentage		101.00%
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.

Segment Reporting Information (

Segment Reporting Information (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Segment Reporting Information, Profit (Loss) [Abstract]
Revenue from external customers	[1],[2],[3]									$ 62,159		$ 59,485		$ 56,977
Net investment income	[3]									910		917		946
Interest expense	[3]									604		369		334
Depreciation and amortization expense	[3]									681		671		629
Income taxes		$ 147	$ 476	$ 561	$ 551	$ 263	$ 461	$ 527	$ 590	1,735	[3]	1,841	[3]	1,455	[3]
Operating earnings (loss)	[3],[4],[5]									2,917		2,717		2,405
Segment assets		$ 69,146				$ 53,509				69,146		53,509
Health Care [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Revenue from external customers	[3]									59,860		57,203		54,677
Net investment income	[3]									458		408		368
Interest expense	[3]									0		0		0
Depreciation and amortization expense	[3]									681		671		627
Income taxes	[3]									1,856		1,908		1,587
Operating earnings (loss)	[3],[5]									2,948		2,712		2,377
Group Insurance [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Revenue from external customers	[3]									2,251		2,240		2,214
Net investment income	[3]									226		238		261
Interest expense	[3]									0		0		0
Depreciation and amortization expense	[3]									0		0		2
Income taxes	[3]									26		38		57
Operating earnings (loss)	[3],[5]									124		136		171
Large Case Pension [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Revenue from external customers	[3]									48		42		86
Net investment income	[3]									226		271		317
Interest expense	[3]									0		0		0
Depreciation and amortization expense	[3]									0		0		0
Income taxes	[3]									44		(9)		1
Operating earnings (loss)	[3],[5]									14		17		21
Corporate Financing [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Revenue from external customers	[3]									0		0		0
Net investment income	[3]									0		0		0
Interest expense	[3]									604		369		334
Depreciation and amortization expense	[3]									0		0		0
Income taxes	[3]									(191)		(96)		(190)
Operating earnings (loss)	[3],[5]									$ (169)		$ (148)		$ (164)
[1]	All within the U.S., except approximately $642 million, $1.3 billion and $1.2 billion in 2016, 2015 and 2014, respectively, which were derived from foreign customers.
[2]	Revenue from the U.S. federal government was approximately $20.5 billion, $17.8 billion and $16.5 billion in 2016, 2015 and 2014, respectively, in the Health Care and Group Insurance segments. These amounts exceeded 10 percent of our total revenue from external customers in each of 2016, 2015 and 2014.
[3]	Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer.
[4]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
[5]	Operating earnings (loss) excludes net realized capital gains or losses, amortization of other acquired intangible assets and the other items described in this Note 18.

Segment Information - Reconcili

Segment Information - Reconciliation of Operating Earnings (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Aetna		$ 139	$ 604	$ 791	$ 737	$ 321	$ 560	$ 732	$ 777	$ 2,271	[1]	$ 2,390	[1]	$ 2,041	[1]
Business Combination, Integration Related Costs	[1]									517		258		201
Segment Reconciliation [Abstract]
Operating earnings	[1],[2],[3]									2,917		2,717		2,405
Litigation-related proceeds, net of tax	[1]									0		(110)		0
Amortization of other acquired intangible assets	[1]									247		255		243
Charges for changes in our life claim payments practices, net of tax																$ (36)
Reduction of reserve for anticipated future losses on discontinued products, after tax										(84)
Net Realized Capital Gains (Losses), Other Item	[1]									(86)		65		(80)
Unusual or Infrequent Item, or Both, Tax Effect	[1]									(308)		(156)		(190)
Restructuring Charges	[1]									404		15		0
Loss on early extinguishment of long-term debt	[1]									0		0		181
Pension settlement charge	[1]									0		0		112
Settlement of class action litigation, after-tax																	$ (78)
Litigation Settlement, Expense																	$ 120
Release of litigation-related reserve, pre-tax	[1]									0		0		(103)
Charge for changes in our life claim payment practices																$ 55
Reduction of reserve for anticipated future losses on discontinued products	[1]									(128)		$ 0		0
Lump-sum distribution percentage [Member] | Pension Settlement Charge [Member]
Segment Reconciliation [Abstract]
Pension Lump Sum Percentage												100.00%
Pension Settlement Charge [Member] | Pension Plan [Member]
Segment Reconciliation [Abstract]
Pension settlement charge										$ 0		$ 0		$ (112)
Pension Plan [Member]
Segment Reconciliation [Abstract]
Pension settlement charge												$ (112)
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
[2]	Operating earnings (loss) excludes net realized capital gains or losses, amortization of other acquired intangible assets and the other items described in this Note 18.
[3]	Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer.

Segment Information - Revenues

Segment Information - Revenues from External Customers by Product (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customer [Line Items]
Revenue from external customers	[1],[2],[3]	$ 62,159	$ 59,485	$ 56,977
Other revenue	[4]	5,861	5,696	5,229
Premiums Earned Net Accident And Health [Member]
Revenue from External Customer [Line Items]
Revenue from external customers		54,116	51,618	49,562
Health Care Fees And Other Revenue [Member]
Revenue from External Customer [Line Items]
Revenue from external customers		5,744	5,585	5,115
Group Life [Member]
Revenue from External Customer [Line Items]
Revenue from external customers		2,143	2,139	2,110
Group Disability [Member]
Revenue from External Customer [Line Items]
Revenue from external customers		108	101	104
Large Case Pension [Member]
Revenue from External Customer [Line Items]
Revenue from external customers		39	32	76
Other revenue	[4]	9	10	10
United States Federal Government [Member]
Revenue from External Customer [Line Items]
Revenue from external customers		20,500	17,800	16,500
Revenue from foreign customers [Member]
Revenue from External Customer [Line Items]
Revenue from external customers		$ 642	$ 1,300	$ 1,200
[1]	All within the U.S., except approximately $642 million, $1.3 billion and $1.2 billion in 2016, 2015 and 2014, respectively, which were derived from foreign customers.
[2]	Revenue from the U.S. federal government was approximately $20.5 billion, $17.8 billion and $16.5 billion in 2016, 2015 and 2014, respectively, in the Health Care and Group Insurance segments. These amounts exceeded 10 percent of our total revenue from external customers in each of 2016, 2015 and 2014.
[3]	Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer.
[4]	Fees and other revenue include administrative services contract member co-payments and plan sponsor reimbursements related to our mail order and specialty pharmacy operations of $128 million, $112 million and $102 million for 2016, 2015 and 2014, respectively (net of pharmaceutical and processing costs of $1.3 billion for each of 2016, 2015 and 2014).

Segment Information - Reconci98

Segment Information - Reconciliation of Revenue from External Customers to Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of revenue from external customers to total revenues [Abstract]
Revenue from external customers	[1],[2],[3]									$ 62,159	$ 59,485	$ 56,977
Net investment income	[3]									910	917	946
Net realized capital gains (losses)										86	(65)	80
Total revenue		$ 15,727	$ 15,782	$ 15,952	$ 15,694	$ 15,049	$ 14,953	$ 15,241	$ 15,094	63,155	60,337	$ 58,003
Long-lived assets, within the United States		$ 579				$ 622				$ 579	$ 622
[1]	All within the U.S., except approximately $642 million, $1.3 billion and $1.2 billion in 2016, 2015 and 2014, respectively, which were derived from foreign customers.
[2]	Revenue from the U.S. federal government was approximately $20.5 billion, $17.8 billion and $16.5 billion in 2016, 2015 and 2014, respectively, in the Health Care and Group Insurance segments. These amounts exceeded 10 percent of our total revenue from external customers in each of 2016, 2015 and 2014.
[3]	Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer.

Discontinued Products (Details)

Discontinued Products (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 1993
Reserve For Discontinued Products [Roll Forward]
Reduction of reserve for anticipated future losses on discontinued products	[1]	$ 128		$ 0		$ 0
Reduction of reserve for anticipated future losses on discontinued products, after tax		84
Assets:
Investments							$ 24,879		$ 24,680
Total assets							69,146		53,509
Liabilities:
Future policy benefits							5,929		6,268
Total liabilities							51,203		37,330
Mortgage loans investment portfolio							$ 370					$ 5,400
Mortgage loans investment portfolio percentages (in hundredths)							13.00%					37.00%
Real Estate investment portfolio							$ 108					$ 500
Real Estate investment portfolio percentages (in hundredths)							4.00%					4.00%
Expected Runoff Of Single Premium Annuities							$ 1,942		2,112		$ 2,281
Expected Runoff Of Guaranteed Investment Contracts Liabilities							9		10		12
Actual Runoff Of Single Premium Annuities							2,326		2,494		2,646
Actual Runoff Of Guaranteed Investment Contracts Liabilities							0		0		0
Scheduled Contract Maturities, Settlements And Benefit Payments		364		356		378
Discontinued Products [Member]
Reserve For Discontinued Products [Roll Forward]
Reserve, beginning of period		1,067	[2]	1,015		980
Operating income (loss)		(34)		(9)		6
Net realized capital gains		57		61.1		29
Reduction of reserve for anticipated future losses on discontinued products		(128)		0		0
Reserve, end of period		962	[2]	1,067	[2]	1,015
Assets:
Investments	[2]						2,929		3,059
Other Assets	[2]						104		129
Current and deferred income taxes	[2]						0		21
Receivable from continuing products	[2],[3]						554		602
Total assets	[2]						3,587		3,811
Liabilities:
Future policy benefits	[2]						2,326		2,494
Reserve for anticipated future losses on discontinued products		1,067	[2]	$ 1,015		$ 980	962	[2]	1,067	[2]	$ 1,015
Current and deferred income tax liabilities	[2]						42		0
Other Liabilities	[2],[4]						257		250
Total liabilities							3,587	[3]	3,811	[2]
Debt And Equity Securities Available For Sale [Member]
Assets:
Investments							21,742		21,323
Debt And Equity Securities Available For Sale [Member] | Discontinued Products [Member]
Assets:
Investments	[2]						1,913		2,020
Mortgage Loans [Member]
Assets:
Investments							1,511		1,554
Mortgage Loans [Member] | Discontinued Products [Member]
Assets:
Investments	[2]						370		396
Other Investments [Member]
Assets:
Investments							1,626		1,803
Other Investments [Member] | Discontinued Products [Member]
Assets:
Investments	[2]						646		$ 643
Single Premium Annuities And Guaranteed Investment Contracts Liabilities [Member]
Liabilities:
2,017							348
2,018							332
2,019							316
2,020							301
2,021							285
Thereafter							3,540
Discontinued Products Reserve Balance [Member]
Liabilities:
2,017							54
2,018							53
2,019							51
2,020							50
2,021							48
Thereafter							$ 706
Before Income Tax Expense (Benefit) [Member]
Reserve For Discontinued Products [Roll Forward]
Reduction of reserve for anticipated future losses on discontinued products		$ 128
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
[2]	Assets supporting the discontinued products are distinguished from assets supporting continuing products.
[3]	At the time of discontinuance, a receivable from Large Case Pensions’ continuing products was established on the discontinued products balance sheet. This receivable represented the net present value of anticipated cash shortfalls in the discontinued products, which will be funded from continuing products. Interest on the receivable is accrued at the discount rate that was used to calculate the reserve. The offsetting payable, on which interest is similarly accrued, is reflected in continuing products. Interest on the payable generally offsets investment income on the assets available to fund the shortfall. These amounts are eliminated in consolidation.
[4]	Net unrealized capital gains on the available-for-sale debt securities are included in other liabilities and are not reflected in consolidated shareholders’ equity.

Quarterly Financial Data (Detai

Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 15,727		$ 15,782		$ 15,952		$ 15,694		$ 15,049		$ 14,953		$ 15,241		$ 15,094		$ 63,155		$ 60,337		$ 58,003
Income before income taxes	275		1,073		1,354		1,289		585		1,023		1,262		1,366		3,991		4,236		3,500
Income taxes	(147)		(476)		(561)		(551)		(263)		(461)		(527)		(590)		(1,735)	[1]	(1,841)	[1]	(1,455)	[1]
Net income including non-controlling interests	128		597		793		738		322		562		735		776		2,256		2,395		2,045
Less: Net income (loss) attributable to non-controlling interests	(11)		(7)		2		1		1		2		3		(1)		(15)		5		4
Net income attributable to the Aetna	$ 139		$ 604		$ 791		$ 737		$ 321		$ 560		$ 732		$ 777		$ 2,271	[2]	$ 2,390	[2]	$ 2,041	[2]
Basic EPS (in dollars per share)	$ 0.40	[3]	$ 1.72	[3]	$ 2.25	[3]	$ 2.10	[3]	$ 0.92	[3]	$ 1.60	[3]	$ 2.10	[3]	$ 2.22	[3]	$ 6.46		$ 6.84		$ 5.74
Diluted EPS (in dollars per share)	0.39	[3]	1.70	[3]	2.23	[3]	2.09	[3]	0.91	[3]	1.59	[3]	2.08	[3]	2.20	[3]	6.41		6.78		$ 5.68
Dividends Amount Per Share	$ 0.250		$ 0.250		$ 0.250		$ 0.250		$ 0.250		$ 0.250		$ 0.250		$ 0.250		$ 0.250		$ 0.250
[1]	Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer.
[2]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
[3]	Calculation of net income attributable to Aetna per share is based on weighted average shares outstanding during each quarter and, accordingly, the sum may not equal the total for the year.

Schedule I_ Financial Informati

Schedule I: Financial Information of Aetna Inc. (Parent Company) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss on early extinguishment of long-term debt	[1]									$ 0		$ 0		$ 181
Current assets: [Abstract]
Cash and cash equivalents		$ 17,996			$ 2,524	$ 2,524			$ 1,420	2,524		1,420		1,412		$ 17,996	$ 2,524	$ 1,420	$ 1,412
Investments																3,046	3,015
Other receivables																2,224	2,307
Income taxes receivable																44	261
Other current assets																2,551	2,510
Total current assets																28,449	12,725
Long-term Investments																21,833	21,665
Other long-term assets																1,480	1,405
Total assets																69,146	53,509
Current liabilities [Abstract]
Accrued expenses and other current liabilities																5,728	4,920
Long-term Debt, Current Maturities																1,634	0
Total current liabilities																18,694	15,609
Long-term debt, less current portion																19,027	7,785
Other long-term liabilities																1,043	914
Total liabilities																51,203	37,330
Shareholders' equity [Abstract]
Common stock ($.01 par value; 2.5 billion shares authorized and 351.7 million shares issued and outstanding in 2016; 2.5 billion shares authorized and 349.5 million shares issued and outstanding in 2015) and additional paid-in capital																4,716	4,647
Retained earnings																14,717	12,797
Accumulated other comprehensive loss																(1,552)	(1,330)
Total Aetna shareholders' equity		17,881			16,114	16,114				16,114		16,114				17,881	16,114
Non-controlling interests																62	65
Total equity																17,943	16,179	14,552	14,078
Total liabilities and equity																$ 69,146	$ 53,509
Common Stock, Par or Stated Value Per Share																$ 0.01	$ 0.01
Common Stock, Shares Authorized																2,500	2,500
Common Stock, Shares, Issued																351.7	349.5
Income Statement [Abstract]
Other revenue	[2]									5,861		5,696		5,229
Net Investment Income	[3]									910		917		946
Realized Investment Gains (Losses)										86		(65)		80
Total revenue		15,727	$ 15,782	$ 15,952	15,694	15,049	$ 14,953	$ 15,241	15,094	63,155		60,337		58,003
Operating Expenses										12,085		11,644		10,833
Interest Expense	[3]									604		369		334
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest		275	1,073	1,354	1,289	585	1,023	1,262	1,366	3,991		4,236		3,500
Income taxes		147	476	561	$ 551	263	461	527	590	$ 1,735	[3]	1,841	[3]	1,455	[3]
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period (in shares)					349.5					349.5
Balance at beginning of period					$ 16,114					$ 16,114
Noncontrolling Interest, Period Increase (Decrease)										12		(9)		12
Less: Net income (loss) attributable to non-controlling interests		(11)	(7)	2	1	1	2	3	(1)	(15)		5		4
Net income including non-controlling interests		128	597	793	738	322	562	735	776	2,256		2,395		2,045
Comprehensive income:
Net income attributable to the Aetna		$ 139	604	791	737	$ 321	560	732	777	2,271	[1]	2,390	[1]	2,041	[1]
Other comprehensive income:
Other comprehensive income (loss)										(222)		(219)		(199)
Comprehensive income attributable to Aetna										2,049		2,171		1,842
Common shares issued for benefit plans, including tax benefits										69		105		160
Repurchases of common shares												(296)		(1,218)
Dividends declared										$ (351)		$ (349)		(326)
Balance at end of period (in shares)		351.7				349.5				351.7		349.5
Balance at end of period		$ 17,881				$ 16,114				$ 17,881		$ 16,114
Cash flows from operating activities: [Abstract]
Net income attributable to the Aetna		139	$ 604	$ 791	737	321	$ 560	$ 732	777	2,271	[1]	2,390	[1]	2,041	[1]
Adjustments to reconcile net income to net cash used for operating activities:
Pension settlement charge	[1]									0		0		112
Equity in earnings of affiliates										(6)		(31)		(40)
Amortization of Interest Rate Hedges										20		6		6
Stock-based compensation expense										191		181		163
Net realized capital (gains) losses										(86)		65		(80)
Net change in other assets and other liabilities										(653)		(644)		(363)
Net cash provided by operating activities										3,719		3,866		3,373
Net cash provided by (used for) operating activities [Abstract]
Proceeds from sales and maturities of investments										14,741		12,299		9,484
Cost of investments										(14,852)		(12,943)		(10,804)
Cash used for acquisitions, net of cash acquired										0		(20)		(440)
Net cash provided by (used for) investing activities										(381)		(1,027)		(2,130)
Cash flows from financing activities: [Abstract]
Net repayment of long-term debt										0		(229)		(1,798)
Issuance of long-term debt										12,886		0		1,482
Net (repayment) issuance of short-term debt										0		(500)		500
Common shares issued under benefit plans, net										(139)		(143)		(60)
Stock-based compensation tax benefits										0		53		41
Common shares repurchased										0		(296)		(1,218)
Net payment on interest rate derivatives										(274)		(25)		(77)
Dividends paid to shareholders										(351)		(349)		(321)
Net cash provided by (used for) financing activities										12,134		(1,735)		(1,235)
Net increase (decrease) in cash and cash equivalents										15,472		1,104		8
Cash and cash equivalents, beginning of period					$ 2,524				$ 1,420	2,524		1,420		1,412
Cash and cash equivalents, end of period		$ 17,996				$ 2,524				17,996		2,524		1,420
Supplemental Cash Flow Information [Abstract]
Interest Paid										541		338		379
Amortization of other acquired intangible assets	[1]									247		255		243
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries										$ 2,900		$ 2,200		$ 1,500
Common Stock [Member]
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period (in shares)					349.5				349.8	349.5		349.8		362.2
Other comprehensive income:
Common shares issued for benefit plans, including tax benefits (in shares)										2.2		2.7		3.5
Repurchases of common shares (in shares)												(3)		(15.9)
Balance at end of period (in shares)		351.7				349.5				351.7		349.5		349.8
Common Stock Including Additional Paid in Capital [Member]
Shareholders' equity [Abstract]
Total Aetna shareholders' equity		$ 4,716			$ 4,647	$ 4,647			$ 4,542	$ 4,647		$ 4,542		$ 4,382		$ 4,716	$ 4,647	4,542	4,382
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period					4,647				4,542	4,647		4,542		4,382
Noncontrolling Interest, Period Increase (Decrease)										0		0		0
Comprehensive income:
Net income attributable to the Aetna										0
Other comprehensive income:
Common shares issued for benefit plans, including tax benefits										69		105		160
Repurchases of common shares												0		0
Balance at end of period		4,716				4,647				4,716		4,647		4,542
Cash flows from operating activities: [Abstract]
Net income attributable to the Aetna										0
Parent [Member]
Shareholders' equity [Abstract]
Total Aetna shareholders' equity		17,881			16,114	16,114			14,483	16,114		14,483		14,025		17,881	16,114	14,483	14,025
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period					16,114				14,483	16,114		14,483		14,025
Noncontrolling Interest, Period Increase (Decrease)										0		0		0
Comprehensive income:
Net income attributable to the Aetna										2,271		2,390		2,041
Other comprehensive income:
Other comprehensive income (loss)										(222)		(219)		(199)
Common shares issued for benefit plans, including tax benefits										69		105		160
Repurchases of common shares												(296)		(1,218)
Dividends declared										(351)		(349)		(326)
Balance at end of period		17,881				16,114				17,881		16,114		14,483
Cash flows from operating activities: [Abstract]
Net income attributable to the Aetna										2,271		2,390		2,041
Noncontrolling Interest [Member]
Shareholders' equity [Abstract]
Non-controlling interests																62	65	69	53
Statement of Stockholders' Equity [Abstract]
Noncontrolling Interest, Period Increase (Decrease)										12		(9)		12
Less: Net income (loss) attributable to non-controlling interests										(15)		5		4
Retained Earnings [Member]
Shareholders' equity [Abstract]
Total Aetna shareholders' equity		14,717			12,797	12,797			11,052	12,797		11,052		10,555		14,717	12,797	11,052	10,555
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period					12,797				11,052	12,797		11,052		10,555
Comprehensive income:
Net income attributable to the Aetna										2,271		2,390		2,041
Other comprehensive income:
Repurchases of common shares												(296)		(1,218)
Dividends declared										(351)		(349)		(326)
Balance at end of period		14,717				12,797				14,717		12,797		11,052
Cash flows from operating activities: [Abstract]
Net income attributable to the Aetna										2,271		2,390		2,041
Accumulated Other Comprehensive Loss [Member]
Shareholders' equity [Abstract]
Total Aetna shareholders' equity		(1,552)			(1,330)	(1,330)			(1,111)	(1,330)		(1,111)		(912)		(1,552)	(1,330)	(1,111)	(912)
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period					(1,330)				(1,111)	(1,330)		(1,111)		(912)
Comprehensive income:
Net income attributable to the Aetna										0
Other comprehensive income:
Other comprehensive income (loss)										(222)		(219)		(199)
Balance at end of period		(1,552)				(1,330)				(1,552)		(1,330)		(1,111)
Cash flows from operating activities: [Abstract]
Net income attributable to the Aetna										0
Parent Company [Member]
Loss on early extinguishment of long-term debt										0		0		181
Current assets: [Abstract]
Cash and cash equivalents		14,972			176	176			18	176		18		188		14,972	176	18	188
Investments																4	0
Other receivables																0	98
Income taxes receivable																48	34
Other current assets																109	197
Total current assets																15,133	505
Investment in affiliates																23,415	23,236
Long-term Investments																0	19
Deferred income taxes																285	270
Other long-term assets																107	88
Total assets																38,940	24,118
Current liabilities [Abstract]
Accrued expenses and other current liabilities																792	626
Long-term Debt, Current Maturities																1,248	0
Total current liabilities																2,040	626
Long-term debt, less current portion																18,366	6,708
Employee benefit liabilities																545	552
Accrued Income Taxes																0	6
Other long-term liabilities																46	47
Total liabilities																20,997	7,939
Shareholders' equity [Abstract]
Common stock ($.01 par value; 2.5 billion shares authorized and 351.7 million shares issued and outstanding in 2016; 2.5 billion shares authorized and 349.5 million shares issued and outstanding in 2015) and additional paid-in capital																4,716	4,647
Retained earnings																14,717	12,797
Accumulated other comprehensive loss																(1,552)	(1,330)
Total Aetna shareholders' equity		$ 17,881			$ 16,114	$ 16,114				16,114		16,114				17,881	16,114
Non-controlling interests																62	65
Total equity																17,943	16,179	14,552	14,078
Total liabilities and equity																$ 38,940	$ 24,118
Common Stock, Par or Stated Value Per Share																$ 0.01	$ 0.01
Common Stock, Shares Authorized																2,500	2,500
Common Stock, Shares, Issued																351.7	349.5
Goodwill and Other Acquired Intangible Assets																$ 12,100	$ 12,300
Income Statement [Abstract]
Other revenue										0		110		0
Net Investment Income										31		0		1
Realized Investment Gains (Losses)										(6)		0		28
Total revenue										25		110		29
Operating Expenses										289		183		275
Interest Expense										578		343		303
Total Expenses										867		526		759
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest										(842)		(416)		(730)
Income taxes										$ (249)		(93)		(248)
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period (in shares)					349.5					349.5
Balance at beginning of period					$ 16,114					$ 16,114
Noncontrolling Interest, Period Increase (Decrease)										12		(9)		12
Net income including non-controlling interests										2,256		2,395		2,045
Comprehensive income:
Net income attributable to the Aetna										2,271		2,390		2,041
Other comprehensive income:
Other comprehensive income (loss)										(222)		(219)		(199)
Comprehensive income attributable to Aetna										2,049		2,171		1,842
Common shares issued for benefit plans, including tax benefits										69		105		160
Repurchases of common shares												(296)		(1,218)
Dividends declared										$ (351)		$ (349)		(326)
Balance at end of period (in shares)		351.7				349.5				351.7		349.5
Balance at end of period		$ 17,881				$ 16,114				$ 17,881		$ 16,114
Cash flows from operating activities: [Abstract]
Net income attributable to the Aetna										2,271		2,390		2,041
Adjustments to reconcile net income to net cash used for operating activities:
Pension settlement charge										0		0		112
Equity in earnings of affiliates										(2,864)		(2,713)		(2,523)
Amortization of Interest Rate Hedges										20		6		6
Stock-based compensation expense										191		181		163
Net realized capital (gains) losses										6		0		(28)
Net change in other assets and other liabilities										308		(245)		127
Net cash provided by operating activities										(68)		(381)		79
Net cash provided by (used for) operating activities [Abstract]
Proceeds from sales and maturities of investments										0		66		18
Cost of investments										0		0		(86)
Dividends received from affiliates, net										2,742		1,733		895
Net cash provided by (used for) investing activities										2,742		1,799		827
Cash flows from financing activities: [Abstract]
Net repayment of long-term debt										0		0		(1,423)
Issuance of long-term debt										12,886		0		1,482
Net (repayment) issuance of short-term debt										0		(500)		500
Common shares issued under benefit plans, net										(139)		(143)		(60)
Stock-based compensation tax benefits										0		53		41
Common shares repurchased										0		(296)		(1,218)
Net payment on interest rate derivatives										(274)		(25)		(77)
Dividends paid to shareholders										(351)		(349)		(321)
Net cash provided by (used for) financing activities										12,122		(1,260)		(1,076)
Net increase (decrease) in cash and cash equivalents										14,796		158		(170)
Cash and cash equivalents, beginning of period					$ 176				$ 18	176		18		188
Cash and cash equivalents, end of period		$ 14,972				$ 176				14,972		176		18
Supplemental Cash Flow Information [Abstract]
Interest Paid										485		276		286
Income taxes refunded										252		282		198
Amortization of other acquired intangible assets										$ 161		$ 166		$ 158
Parent Company [Member] | Common Stock [Member]
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period (in shares)					349.5				349.8	349.5		349.8		362.2
Other comprehensive income:
Common shares issued for benefit plans, including tax benefits (in shares)										2.2		2.7		3.5
Repurchases of common shares (in shares)												(3)		(15.9)
Balance at end of period (in shares)		351.7				349.5				351.7		349.5		349.8
Parent Company [Member] | Common Stock Including Additional Paid in Capital [Member]
Shareholders' equity [Abstract]
Total Aetna shareholders' equity		$ 4,716			$ 4,647	$ 4,647			$ 4,542	$ 4,647		$ 4,542		$ 4,382		4,716	4,647	4,542	4,382
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period					4,647				4,542	4,647		4,542		4,382
Noncontrolling Interest, Period Increase (Decrease)										0		0		0
Other comprehensive income:
Common shares issued for benefit plans, including tax benefits										69		105		160
Repurchases of common shares												0		0
Balance at end of period		4,716				4,647				4,716		4,647		4,542
Parent Company [Member] | Parent [Member]
Shareholders' equity [Abstract]
Total Aetna shareholders' equity		17,881			16,114	16,114			14,483	16,114		14,483		14,025		17,881	16,114	14,483	14,025
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period					16,114				14,483	16,114		14,483		14,025
Noncontrolling Interest, Period Increase (Decrease)										0		0		0
Comprehensive income:
Net income attributable to the Aetna										2,271		2,390		2,041
Other comprehensive income:
Other comprehensive income (loss)										(222)		(219)		(199)
Common shares issued for benefit plans, including tax benefits										69		105		160
Repurchases of common shares												(296)		(1,218)
Dividends declared										(351)		(349)		(326)
Balance at end of period		17,881				16,114				17,881		16,114		14,483
Cash flows from operating activities: [Abstract]
Net income attributable to the Aetna										2,271		2,390		2,041
Parent Company [Member] | Noncontrolling Interest [Member]
Shareholders' equity [Abstract]
Non-controlling interests																62	65	69	53
Statement of Stockholders' Equity [Abstract]
Noncontrolling Interest, Period Increase (Decrease)										12		(9)		12
Less: Net income (loss) attributable to non-controlling interests										(15)		5		4
Parent Company [Member] | Retained Earnings [Member]
Shareholders' equity [Abstract]
Total Aetna shareholders' equity		14,717			12,797	12,797			11,052	12,797		11,052		10,555		14,717	12,797	11,052	10,555
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period					12,797				11,052	12,797		11,052		10,555
Comprehensive income:
Net income attributable to the Aetna										2,271		2,390		2,041
Other comprehensive income:
Repurchases of common shares												(296)		(1,218)
Dividends declared										(351)		(349)		(326)
Balance at end of period		14,717				12,797				14,717		12,797		11,052
Cash flows from operating activities: [Abstract]
Net income attributable to the Aetna										2,271		2,390		2,041
Parent Company [Member] | Accumulated Other Comprehensive Loss [Member]
Shareholders' equity [Abstract]
Total Aetna shareholders' equity		(1,552)			(1,330)	(1,330)			(1,111)	(1,330)		(1,111)		(912)		$ (1,552)	$ (1,330)	$ (1,111)	$ (912)
Statement of Stockholders' Equity [Abstract]
Balance at beginning of period					$ (1,330)				$ (1,111)	(1,330)		(1,111)		(912)
Other comprehensive income:
Other comprehensive income (loss)										(222)		(219)		(199)
Balance at end of period		$ (1,552)				$ (1,330)				(1,552)		(1,330)		(1,111)
Net Unrealized Gains (Losses) Previously Impaired Securities [Member]
Other comprehensive income:
Other comprehensive income (loss)	[4]									(3)		(16)		1
Net Unrealized Gains (Losses) Previously Impaired Securities [Member] | Parent Company [Member]
Other comprehensive income:
Other comprehensive income (loss)										(3)		(16)		1
Net Unrealized Gains (Losses) All Other Securities [Member]
Other comprehensive income:
Other comprehensive income (loss)										(15)		(256)		241
Net Unrealized Gains (Losses) All Other Securities [Member] | Parent Company [Member]
Other comprehensive income:
Other comprehensive income (loss)										(15)		(256)		241
Derivatives [Member]
Other comprehensive income:
Other comprehensive income (loss)										(161)		(13)		(61)
Derivatives [Member] | Parent Company [Member]
Other comprehensive income:
Other comprehensive income (loss)										(161)		(13)		(61)
Pension and OPEB Plan [Member]
Other comprehensive income:
Other comprehensive income (loss)										(43)		66		(380)
Pension and OPEB Plan [Member] | Parent Company [Member]
Other comprehensive income:
Other comprehensive income (loss)										$ (43)		$ 66		$ (380)
[1]	In addition to net realized capital gains and losses and amortization of other acquired intangible assets, the following other items are excluded from operating earnings because we believe they neither relate to the ordinary course of our business nor reflect our underlying business performance:•We incurred transaction and integration-related costs during 2016 and 2015 related to the acquisitions of Coventry, InterGlobal, bswift and the proposed Humana Acquisition. We incurred transaction and integration-related costs during 2014 related to the acquisitions of Coventry, bswift and InterGlobal. Transaction costs include advisory, legal and other professional fees which are not deductible for tax purposes and are reflected in our GAAP Consolidated Statements of Income in general and administrative expenses, as well as the cost of the Bridge Credit Agreement and the Term Loan Agreement executed in connection with the proposed Humana Acquisition, which are reflected in our GAAP Consolidated Statements of Income in interest expense. Transaction costs also include the negative cost of carry associated with the 2016 senior notes. Prior to the termination of the Merger Agreement, the negative cost of carry associated with the 2016 senior notes was excluded from operating earnings. The components of the negative cost of carry are reflected in our GAAP Consolidated Statements of Income in interest expense and net investment income. Subsequent to the termination of the Merger Agreement, the interest expense and net investment income associated with the 2016 senior notes no longer will be excluded from operating earnings. •Restructuring costs for 2016 include costs related to our voluntary early retirement program, severance and real estate consolidation costs associated with our expense management and cost control initiative and an accrual for minimum volume commitments which require us to make payments to suppliers if the level of medical membership subject to the agreements falls below specified levels. We no longer expect to meet these minimum volume commitments as a result of our previously announced reduced participation on the ACA’s individual Public Exchanges in 2017. Restructuring costs for 2015 include severance costs associated with our expense management and cost control initiative. The 2016 and 2015 restructuring costs are reflected in the GAAP Consolidated Statements of Income in general and administrative expenses.•In 1993, we discontinued the sale of our fully guaranteed large case pensions products and established a reserve for anticipated future losses on these products, which we review quarterly. During 2016, we reduced the reserve for anticipated future losses on discontinued products. We believe excluding any changes in the reserve for anticipated future losses on discontinued products from operating earnings provides more useful information as to our continuing products and is consistent with the treatment of the operating results of these discontinued products, which are credited or charged to the reserve and do not affect our operating results. Refer to Note 19 for additional information on the reduction of the reserve for anticipated future losses on discontinued products.•In 2015, we received proceeds net of legal costs, in connection with a litigation settlement. These net proceeds were recorded in fees and other revenue in our GAAP Consolidated Statements of Income.•In 2014, we incurred losses on the early extinguishment of long-term debt related to the redemption of certain of our outstanding senior notes.•During 2014, we enhanced the Aetna Pension Plan to allow certain current and former employees to elect a 100% lump-sum distribution. In addition, we also announced a limited-time offer permitting certain former employees with deferred vested balances to elect a 100% lump-sum distribution. The distributions in 2014 were funded from existing Aetna Pension Plan assets, and we recorded a related non-cash settlement charge during 2014 in general and administrative expenses. Refer to Note 10 for additional information on the pension settlement charge. •In 2012, we recorded a charge related to the settlement of purported class action litigation regarding our payment practices related to out-of-network health care providers. That charge included the estimated cost of legal fees of plaintiffs’ counsel and the costs of administering the settlement. In 2014, we exercised our right to terminate the settlement agreement. As a result, we released the reserve established in connection with the settlement agreement, net of amounts due to the settlement administrator, which reduced 2014 other general and administrative expenses. Refer to Note 17 for additional information on the termination of the settlement agreement.•The corresponding tax benefit or expense related to the items excluded from operating earnings discussed above. The tax benefit or expense was calculated utilizing the appropriate tax rate for each individual item excluded from operating earnings.
[2]	Fees and other revenue include administrative services contract member co-payments and plan sponsor reimbursements related to our mail order and specialty pharmacy operations of $128 million, $112 million and $102 million for 2016, 2015 and 2014, respectively (net of pharmaceutical and processing costs of $1.3 billion for each of 2016, 2015 and 2014).
[3]	Total assets by segment are not disclosed as this information is not reviewed by the Chief Executive Officer.
[4]	Represents specifically identified unrealized gains on the non-credit related component of impaired debt securities that we do not intend to sell and subsequent changes in the fair value of any previously impaired security.