Income Taxes - Reconciliation of Beginning and Ending Balances of Total Amounts of Gross Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Beginning balance	$ 130	$ 53	$ 48
International operation acquired amounts	0	71	0
Additions to prior years' tax positions	1	0	1
Reductions to prior years' tax positions	(12)	(1)	(2)
Additions to current year tax positions	7	12	9
Reductions in tax positions due to lapse of statutory limitations	(6)	(3)	0
Settlements	(20)	(1)	(3)
Foreign currency translation	(5)	(1)	0
Ending balance	$ 95	$ 130	$ 53