Segment Information - Segment Financial Information (Details) - USD ($) $ in Millions	3 Months Ended											12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Premiums												$ 29,642	$ 27,214	$ 25,575
Fees and other revenues												4,488	4,141	3,601
Net investment income												1,153	1,166	1,164
Mail order pharmacy revenues												2,536	2,239	1,827
Total operating revenues												37,819	34,760	32,167
Realized investment gains (losses)												57	154	213
Total revenues	$ 9,528		$ 9,389		$ 9,492		$ 9,467	$ 8,928	$ 8,757	$ 8,733	$ 8,496	37,876	34,914	32,380
Depreciation and amortization												585	588	597
Total benefits and expenses												34,549	31,610	30,204
Income before income taxes	659		878		936		854	732	818	901	853	3,327	3,304	2,176
Income taxes and net income (loss) attributable to noncontrolling interets												1,233	1,202	700
Shareholders' Net Income	$ 426	[1]	$ 547	[1]	$ 588	[2]	$ 533	$ 467	$ 534	$ 573	$ 528	2,094	2,102	1,476
Operating Segments [Member] | Global Health Care [Member]
Segment Reporting Information [Line Items]
Premiums												22,696	20,709	19,626
Fees and other revenues												4,357	4,005	3,518
Net investment income												340	337	325
Mail order pharmacy revenues												2,536	2,239	1,827
Total operating revenues												29,929	27,290	25,296
Realized investment gains (losses)												43	79	113
Total revenues												29,972	27,369	25,409
Depreciation and amortization												526	513	529
Total benefits and expenses												27,028	24,610	22,957
Income before income taxes												2,944	2,759	2,452
Income taxes and net income (loss) attributable to noncontrolling interets												1,150	1,059	862
Shareholders' Net Income												1,794	1,700	1,590
Operating Segments [Member] | Global Supplemental Benefits [Member]
Segment Reporting Information [Line Items]
Premiums												3,000	2,844	2,496
Fees and other revenues												46	52	43
Net investment income												103	109	100
Mail order pharmacy revenues												0	0	0
Total operating revenues												3,149	3,005	2,639
Realized investment gains (losses)												0	3	3
Total revenues												3,149	3,008	2,642
Depreciation and amortization												31	50	50
Total benefits and expenses												2,849	2,734	2,412
Income before income taxes												300	274	230
Income taxes and net income (loss) attributable to noncontrolling interets												33	41	50
Shareholders' Net Income												267	233	180
Operating Segments [Member] | Group Disability And Life [Member]
Segment Reporting Information [Line Items]
Premiums												3,843	3,549	3,348
Fees and other revenues												91	86	78
Net investment income												337	335	321
Mail order pharmacy revenues												0	0	0
Total operating revenues												4,271	3,970	3,747
Realized investment gains (losses)												5	22	62
Total revenues												4,276	3,992	3,809
Depreciation and amortization												26	22	14
Total benefits and expenses												3,796	3,513	3,387
Income before income taxes												480	479	422
Income taxes and net income (loss) attributable to noncontrolling interets												152	148	123
Shareholders' Net Income												328	331	299
Operating Segments [Member] | Other Operations Segment [Member]
Segment Reporting Information [Line Items]
Premiums												103	112	105
Fees and other revenues												13	14	(24)
Net investment income												369	384	408
Mail order pharmacy revenues												0	0	0
Total operating revenues												485	510	489
Realized investment gains (losses)												9	15	35
Total revenues												494	525	524
Depreciation and amortization												1	2	1
Total benefits and expenses												374	413	1,120
Income before income taxes												120	112	(596)
Income taxes and net income (loss) attributable to noncontrolling interets												40	33	(225)
Shareholders' Net Income												80	79	(371)
Corporate [Member]
Segment Reporting Information [Line Items]
Premiums												0	0	0
Fees and other revenues												(19)	(16)	(14)
Net investment income												4	1	10
Mail order pharmacy revenues												0	0	0
Total operating revenues												(15)	(15)	(4)
Realized investment gains (losses)												0	35	0
Total revenues												(15)	20	(4)
Depreciation and amortization												1	1	3
Total benefits and expenses												502	340	328
Income before income taxes												(517)	(320)	(332)
Income taxes and net income (loss) attributable to noncontrolling interets												(142)	(79)	(110)
Shareholders' Net Income												$ (375)	$ (241)	$ (222)

[1] Shareholders’ net income includes after-tax charges of $29 million in the third quarter of 2015 and $28 million in the fourth quarter of 2015 for advisory, legal and other transactions costs directly related to the Company’s proposed merger with Anthem. See Note 3 to the Consolidated Financial Statements for additional details.

[2] 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 15 to the Consolidated Financial Statements for additional details.