Schedule II - Condensed Financial Information, Statements of Income (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
Operating expenses:
Loss on extinguishment of debt																	$ 0	$ 100	$ 0
Total operating expenses																	9,584	8,982	8,174
Income before Income Taxes		$ 605		$ 742		$ 813		$ 819		$ 659		$ 878		$ 936		$ 854	2,979	3,327	3,304
Income tax expense (benefit)																	1,136	1,250	1,210
Shareholders' Net Income		$ 382	[1],[2]	$ 456	[1],[3]	$ 510	[1]	$ 519	[1]	$ 426	[1]	$ 547	[1]	$ 588	[4]	$ 533	1,867	2,094	2,102
Shareholders' other comprehensive income (loss), net of tax:
Net unrealized appreciation (depreciation) on securities																	(56)	(202)	143
Net unrealized appreciation (depreciation) on derivatives																	(4)	15	11
Net translation of foreign currencies																	(95)	(212)	(144)
Postretirement benefits liability adjustment																	23	85	(426)
Shareholders' other comprehensive income (loss)																	(132)	(314)	(416)
Shareholders' comprehensive income (loss)																	1,735	1,780	1,686
Parent Company [Member]
Operating expenses:
Interest																	244	246	258
Intercompany interest																	3	2	5
Loss on extinguishment of debt																	0	100	0
Other																	281	147	82
Total operating expenses																	528	495	345
Income before Income Taxes																	(528)	(495)	(345)
Income tax expense (benefit)	[5]																(146)	(135)	(89)
(Loss) of parent company	[5]																(382)	(360)	(256)
Equity in income from subsidiaries																	2,249	2,454	2,358
Shareholders' Net Income	[5]																1,867	2,094	2,102
Shareholders' other comprehensive income (loss), net of tax:
Net unrealized appreciation (depreciation) on securities																	(56)	(202)	143
Net unrealized appreciation (depreciation) on derivatives																	(4)	15	11
Net translation of foreign currencies																	(95)	(212)	(144)
Postretirement benefits liability adjustment																	23	85	(426)
Shareholders' other comprehensive income (loss)																	(132)	(314)	(416)
Shareholders' comprehensive income (loss)	[5]																$ 1,735	$ 1,780	$ 1,686

[1] Shareholders’ net income includes after-tax charges related to the Company’s proposed merger with Anthem as follows: $29 million in the third quarter of 2015, $28 million in the fourth quarter of 2015, $36 million in the first quarter of 2016, $26 million in the second quarter of 2016, $46 million in the third quarter of 2016 and $39 million in the fourth quarter of 2016. See Note 3 to the Consolidated Financial Statements for additional details.

[2] Shareholders’ net income includes an after-tax charge of $80 million for an allowance for the risk corridor receivable balance in the fourth quarter of 2016. See Note 22 to the Consolidated Financial Statements for additional details.

[3] Shareholders’ net income includes an after-tax charge of $25 million for charges related to litigation matters in the third quarter of 2016. See Note 21 to the Consolidated Financial Statements for a description of litigation matters.

[4] Shareholders’ net income includes an after-tax charge of $65 million for the early extinguishment of debt in the second quarter of 2015. See Note 5 to the Consolidated Financial Statements for additional details.

[5] As required by the adoption of Accounting Standards Update 2016-09, the Company recorded $29 million of income tax benefits for the year ended December 31, 2016 that previously would have been reported in additional paid-in capital. No retrospective adjustments were made to income tax benefits for the years ended 2015 and 2014. See Note 1 for further discussion.