Borrowings - Senior Secured Revolving Credit Facility (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Jun. 02, 2015	Jun. 01, 2015	Dec. 31, 2014
Senior secured revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 1,250,000,000.00	$ 1,000,000,000.0
Letters of credit outstanding amount	$ 42,000,000			$ 43,000,000
Remaining borrowing capacity	$ 1,200,000,000
Weighted average interest rate	4.60%			5.14%
Commitment fee rate for unused portion of facility (as a percent)	0.50%
Senior secured revolving credit facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.50%
Senior secured revolving credit facility | Base rate
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.50%
Letters of credit
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 250,000,000
Letters of credit outstanding amount	$ 42,000,000