Segment Information - Segment Financial Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Premiums, fees and other revenues and mail order pharmacy revenues	$ 9,644	$ 9,118
Net investment income	272	276
Total operating revenues	9,916	9,394
Total revenues	9,884	9,467
Operating Segments [Member] | Global Health Care [Member]
Segment Reporting Information [Line Items]
Premiums, fees and other revenues and mail order pharmacy revenues	7,812	7,371
Net investment income	72	75
Total operating revenues	7,884	7,446
Total revenues	7,867	7,495
Operating Segments [Member] | Global Supplemental Benefits [Member]
Segment Reporting Information [Line Items]
Premiums, fees and other revenues and mail order pharmacy revenues	780	743
Net investment income	26	26
Total operating revenues	806	769
Total revenues	804	772
Operating Segments [Member] | Group Disability And Life [Member]
Segment Reporting Information [Line Items]
Premiums, fees and other revenues and mail order pharmacy revenues	1,029	976
Net investment income	80	83
Total operating revenues	1,109	1,059
Total revenues	1,106	1,081
Operating Segments [Member] | Other Operations Segment [Member]
Segment Reporting Information [Line Items]
Premiums, fees and other revenues and mail order pharmacy revenues	27	32
Net investment income	90	92
Total operating revenues	117	124
Total revenues	107	123
Corporate [Member]
Segment Reporting Information [Line Items]
Premiums, fees and other revenues and mail order pharmacy revenues	(4)	(4)
Net investment income	4	0
Total operating revenues	0	(4)
Total revenues	$ 0	$ (4)