Segment Information - Summarized Financial Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	$ 7,665	$ 7,143	$ 15,422	$ 13,596
Realized investment gains (losses) from continuing operations, net of taxes and noncontrolling interest	17	(3)	110	9
Shareholders' net income	505	380	562	751
Operating Segments [Member]
Segment Reporting Information [Line Items]
Shareholders' net income	488	383	452	742
Global Heath Care Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	6,171	5,859	12,468	11,165
Shareholders' net income	379	368	806	644
Global Supplemental Benefits Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	622	458	1,234	910
Shareholders' net income	49	27	104	70
Group Disability And Life Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	847	767	1,705	1,530
Shareholders' net income	104	91	102	159
Run Off Reinsurance Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	(1)	37	(38)	(53)
Shareholders' net income	(3)	(62)	(486)	(32)
Other Operations Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	38	39	76	78
Shareholders' net income	18	21	39	41
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	(12)	(17)	(23)	(34)
Shareholders' net income	(59)	(62)	(113)	(140)
Unallocated Amount to Segment [Member]
Segment Reporting Information [Line Items]
Realized investment gains (losses) from continuing operations, net of taxes and noncontrolling interest	$ 17	$ (3)	$ 110	$ 9