Debt (Senior Credit Facilities Narrative) (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended
		Jul. 15, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Debt Instrument [Line Items]
Refinancing expense			$ 4	$ 0	$ 6	$ 0
Senior Unsecured Term Loan Due 2021 [Member]
Debt Instrument [Line Items]
Senior unsecured debt	[1]	$ 500	500		500		$ 0
Senior Unsecured Term Loan Due 2021 and Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Issuance Costs, Gross	[1]		5		5
Secured Debt [Member]
Debt Instrument [Line Items]
Refinancing expense	[1]		$ 4
Revolving Credit Facility [Member] | Senior Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing base	[2]	1,000
Proceeds from lines of credit		$ 409			$ 409

[1] The margin for borrowings under the senior unsecured term loan due 2021 was 1.5% above LIBOR.

[2] The margin for borrowings under the senior unsecured revolving credit facility was 1.5% above LIBOR.