Segment Information - Schedule of Reconciliation of Reportable Segment Depreciation and Amortization Amounts to the Consolidated Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of reportable segment depreciation and amortization amounts to the consolidated balances
Segment depreciation and amortization	$ 999	$ 1,032	$ 1,091
Amortization of initial payments for new contracts	51	45	42
Total consolidated depreciation and amortization per consolidated statements of cash flows	1,133	1,163	1,212
Amortization of equity method investment	(60)	(62)	(79)
Amortization of initial payments for new contracts	(51)	(45)	(42)
Depreciation and amortization	1,022	1,056	1,091
Adjustments
Reconciliation of reportable segment depreciation and amortization amounts to the consolidated balances
Adjustments for non wholly owned entities	83	86	79
Amortization of initial payments for new contracts	51	45	42
Amortization of equity method investment	(60)	(62)	(79)
Amortization of initial payments for new contracts	(51)	(45)	(42)
Depreciation and amortization	$ 1,022	$ 1,056	$ 1,091