Earnings Per Share (Details) (USD $) In Millions, except 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
Earnings Per Share [Abstract]
Shareholders' net income	$ 467	$ 534	$ 573	$ 528	$ 361	[1]	$ 553	$ 505	[2]	$ 57	[3]	$ 2,102	$ 1,476	$ 1,623
Shares (in thousands):
Weighted average												263,889,000	279,296,000	284,819,000
Common stock equivalents												4,714,000	5,389,000	4,711,000
Total shares												268,603,000	284,685,000	289,530,000
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, effect of dilution												$ (0.14)	$ (0.10)	$ (0.09)
EPS, diluted	$ 1.77	$ 2.01	$ 2.12	$ 1.92	$ 1.29		$ 1.95	$ 1.76		$ 0.20		$ 7.83	$ 5.18	$ 5.61
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive options												1,000,000	900,000	2,500,000
Common shares held in Treasury	36,869,000				90,619,000							36,869,000	90,619,000	80,316,000

[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.