Mergers and Acquistions (Details) $ / shares in Units, $ in Millions	3 Months Ended		20 Months Ended
	Mar. 31, 2017 USD ($) $ / shares	Mar. 31, 2016 USD ($)	Mar. 31, 2017 USD ($) $ / shares	May 04, 2017 $ / shares
Acquisitions and Dispositions [Abstract]
Cash consideration for each share of Company stock | $ / shares	$ 103.40		$ 103.40
Shares of acquirer common stock for each share of Company stock	0.5152		0.5152
Closing price of Anthem common stock | $ / shares				$ 179.89
Merger-related costs, before tax	$ 63	$ 40	$ 295
Merger-related costs, after-tax	49	$ 36
Merger agreement not consummated [Member]
Gain Contingencies [Line Items]
Tax benefit if merger is not consummated	$ 60		$ 60