Income Taxes - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Decrease in valuation allowance	$ 78,000,000
Adjustment to additional paid-in-capital for income tax benefits attributable to employee stock compensation	89,000,000	74,000,000	33,000,000
Deferred tax liabilities from undistributed foreign earnings	28,000,000	51,000,000
Undistributed foreign earnings	2,200,000,000
Benefit realized from tax holiday granted	7,000,000	3,000,000	0
Earnings per share impact of tax holiday	$ 0.02	$ 0.01	$ 0.00
Unrecognized tax benefits that would impact effective tax rate	154,000,000	141,000,000	156,000,000
Accrued potential interest and penalties	4,000,000	2,000,000	6,000,000
Liability recorded for interest and penalties	31,000,000	27,000,000	23,000,000
U.K. [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	154,000,000	660,000,000
Capital loss carryforwards	380,000,000	270,000,000
U.S. Federal [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	18,000,000	25,000,000
U.S. State [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	451,000,000	412,000,000
Other [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	325,000,000	287,000,000
Capital loss carryforwards	$ 223,000,000	$ 86,000,000