Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs		$ 1,659	$ 1,502	$ 1,395
Future policy benefits and contractholder deposit funds		17,922	18,072	17,776
Medical claims payable and unpaid claims		6,929	6,580	6,348
Unearned premiums		629	621	580
Premiums	[1]	29,642	27,214	25,575
Net investment income	[2]	1,153	1,166	1,164
Benefit expenses	[1],[3]	23,290	21,334	20,865
Amortization of deferred policy acquisition expenses		286	289	255
Other operating expenses	[4]	10,973	9,987	9,084
Corporate [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs		0	0	0
Future policy benefits and contractholder deposit funds		0	0	0
Medical claims payable and unpaid claims		(6)	(5)	(6)
Unearned premiums		0	0	0
Premiums	[1]	0	0	0
Net investment income	[2]	4	1	10
Benefit expenses	[1],[3]	0	0	0
Amortization of deferred policy acquisition expenses		0	0	0
Other operating expenses	[4]	502	340	328
Global Health Care [Member] | Operating Segments [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs		11	17	20
Future policy benefits and contractholder deposit funds		169	182	197
Medical claims payable and unpaid claims		2,355	2,180	2,050
Unearned premiums		145	155	116
Premiums	[1]	22,696	20,709	19,626
Net investment income	[2]	340	337	325
Benefit expenses	[1],[3]	18,354	16,694	15,867
Amortization of deferred policy acquisition expenses		53	73	69
Other operating expenses	[4]	8,621	7,843	7,021
Global Supplemental Benefits [Member] | Operating Segments [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs		1,593	1,437	1,323
Future policy benefits and contractholder deposit funds		3,006	2,785	2,525
Medical claims payable and unpaid claims		353	339	305
Unearned premiums		453	431	419
Premiums	[1]	3,000	2,844	2,496
Net investment income	[2]	103	109	100
Benefit expenses	[1],[3]	1,659	1,544	1,310
Amortization of deferred policy acquisition expenses		227	209	178
Other operating expenses	[4]	963	981	924
Group Disability And Life [Member] | Operating Segments [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs		1	1	1
Future policy benefits and contractholder deposit funds		1,714	1,662	1,615
Medical claims payable and unpaid claims		4,012	3,844	3,739
Unearned premiums		13	15	23
Premiums	[1]	3,843	3,549	3,348
Net investment income	[2]	337	335	321
Benefit expenses	[1],[3]	2,934	2,716	2,621
Amortization of deferred policy acquisition expenses		1	1	1
Other operating expenses	[4]	861	796	765
Other Operations [Member] | Operating Segments [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs		54	47	51
Future policy benefits and contractholder deposit funds		13,033	13,443	13,439
Medical claims payable and unpaid claims		215	222	260
Unearned premiums		18	20	22
Premiums	[1]	103	112	105
Net investment income	[2]	369	384	408
Benefit expenses	[1],[3]	343	380	1,067
Amortization of deferred policy acquisition expenses		5	6	7
Other operating expenses	[4]	$ 26	$ 27	$ 46

[1] Amounts presented are shown net of the effects of reinsurance. See Note 7 to the Consolidated Financial Statements included in this Form 10-K.

[2] The allocation of net investment income is based upon the investment year method, the identification of certain portfolios with specific segments, or a combination of both.

[3] Benefit expenses include Global Health Care medical cost expense and other benefit expenses.

[4] Other operating expenses include mail order pharmacy costs and other operating expenses, and excludes amortization of deferred policy acquisition expenses.