Segment Information - Summarized Financial Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	$ 9,118	$ 8,177
Net realized investment gains (losses)	48	27
Amortization of other acquired intangible assets, net of taxes	(28)	(32)
Shareholders' net income	533	528
Operating Segments [Member]
Segment Reporting Information [Line Items]
Adjusted income from operations	584	608
Operating Segments [Member] | Global Health Benefits Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	7,371	6,546
Adjusted income from operations	444	467
Operating Segments [Member] | Global Supplemental Benefits Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	743	690
Adjusted income from operations	69	57
Operating Segments [Member] | Group Disability And Life Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	976	915
Adjusted income from operations	51	67
Operating Segments [Member] | Other Operations Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	32	30
Adjusted income from operations	20	17
Corporate And Eliminations Non Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	(4)	(4)
Adjusted income from operations	$ (71)	$ (75)