Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended											12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Shareholders' net income	$ 426	[1]	$ 547	[1]	$ 588	[2]	$ 533	$ 467	$ 534	$ 573	$ 528	$ 2,094	$ 2,102	$ 1,476
Shares:
Weighted average												256,149	263,889	279,296
Common stock equivalents												4,443	4,714	5,389
Total shares												260,592	268,603	284,685
EPS, basic	$ 1.66		$ 2.14		$ 2.30		$ 2.08	$ 1.80	$ 2.04	$ 2.16	$ 1.96	$ 8.17	$ 7.97	$ 5.28
EPS, effect of dilution												(0.13)	(0.14)	(0.10)
EPS, diluted	$ 1.64		$ 2.10		$ 2.26		$ 2.04	$ 1.77	$ 2.01	$ 2.12	$ 1.92	$ 8.04	$ 7.83	$ 5.18
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive options												400	1,000	900

[1] Shareholders’ net income includes after-tax charges of $29 million in the third quarter of 2015 and $28 million in the fourth quarter of 2015 for advisory, legal and other transactions costs directly related to the Company’s proposed merger with Anthem. See Note 3 to the Consolidated Financial Statements for additional details.

[2] Shareholders’ net income includes an after-tax charge of $65 million for the early extinguishment of debt in the second quarter of 2015. See Note 15 to the Consolidated Financial Statements for additional details.