Segment Information - Concentration Risk (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Concentration Risk [Line Items]
Premiums, accounts and notes receivable, net	$ 3,804		$ 2,757
Government Contracts Concentration Risk [Member] | CMS [Member]
Concentration Risk [Line Items]
Premiums, accounts and notes receivable, net	1,400		800
Government Risk Mitigation Programs Concentration Risk [Member] | CMS [Member]
Concentration Risk [Line Items]
Premiums, accounts and notes receivable, net	$ 400		$ 300
Revenue Consolidated [Member] | Government Contracts Concentration Risk [Member] | CMS [Member]
Concentration Risk [Line Items]
Concentration percentage	21.00%	21.00%