Debt (Schedule of Revolving Credit Facility) (Details) - Revolving Credit Facility [Member] - USD ($) $ in Millions			3 Months Ended
		Mar. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Borrowings outstanding	[1]	$ 247	$ 247	$ 40
Senior Unsecured Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Proceeds from Lines of Credit			371
Repayments of Lines of Credit			161
Borrowings outstanding	[2]	247	247
Letters of credit issued		0	0
Available for borrowing	[3]	$ 1,003	$ 1,003
London Interbank Offered Rate (LIBOR) [Member] | Senior Unsecured Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.50%

[1] The weighted average interest rate was 1.5% and 6.0% as of March 31, 2019 and December 31, 2018, respectively.

[2] The Company borrowed $371 million and repaid $161 million under its senior unsecured revolving credit facility during the three months ended March 31, 2019.

[3] The margin for borrowings under the senior unsecured revolving credit facility was 1.5% above LIBOR or EURIBOR at current Company credit ratings.