Quarterly Financial Data (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended											12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Consolidated Quarterly Results [Abstract]
Total revenues	$ 8,928	$ 8,757	$ 8,733	$ 8,496	$ 8,151		$ 8,066	$ 7,980		$ 8,183		$ 34,914	$ 32,380	$ 29,119
Income before income taxes	732	818	901	853	536		799	767		74		3,304	2,176	2,477
Shareholders' net income	467	534	573	528	361	[1]	553	505	[2]	57	[3]	2,102	1,476	1,623
Shareholders' Net Income Per Share:
EPS, basic	$ 1.80	$ 2.04	$ 2.16	$ 1.96	$ 1.32		$ 1.99	$ 1.79		$ 0.20		$ 7.97	$ 5.28	$ 5.70
EPS, diluted	$ 1.77	$ 2.01	$ 2.12	$ 1.92	$ 1.29		$ 1.95	$ 1.76		$ 0.20		$ 7.83	$ 5.18	$ 5.61
Stock And Dividend Data [Abstract]
Price Range Common Stock High	$ 105.73	$ 97.28	$ 93.20	$ 90.63	$ 88.57		$ 84.68	$ 73.13		$ 63.19
Price Range Common Stock Low	$ 85.75	$ 87.33	$ 73.47	$ 75.37	$ 72.64		$ 71.12	$ 61.88		$ 53.91
Dividends Declared Per Share	$ 0	$ 0	$ 0	$ 0.04	$ 0		$ 0	$ 0		$ 0.04		$ 0.04	$ 0.04	$ 0.04
Quarterly Financial Data Text Details [Abstract]
GMIB (gain) loss										(25)
Charge for reinsurance transaction										507
Charge related to regulatory matters										51
Charge related to partnership agreement								24
Charges associated with an organizational efficiency plan					$ 40

[1] The fourth quarter of 2013 includes an after-tax charge of $40 million for an organizational efficiency plan.

[2] The second quarter of 2013 includes an after-tax charge of $24 million for the Pharmacy Benefits Manager (“PBM”) partnering agreement with Catamaran.

[3] The first quarter of 2013 includes an after-tax gain of $25 million for the GMIB business, an after-tax charge of $507 million for the transaction with Berkshire to effectively exit the Run-off Reinsurance business, and an after-tax charge of $51 million related to the disability claims regulatory matter in the Group Disability and Life segment.