Summary of Significant Accounting Policies - Schedule of Amounts Associated with Amortization of Initial Payments for New Contracts and Equity Method Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Amortization of initial payments for new contracts	$ 51	$ 45	$ 42
Amortization related to equity method investments	$ 60	$ 62	$ 79