Debt (Schedule of Revolving Credit Facility) (Details) - Revolving Credit Facility [Member] - USD ($) $ in Millions			6 Months Ended
		Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Repayments of Lines of Credit			$ 156
Borrowings outstanding	[1]	$ 148	148	$ 40
Senior Unsecured Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Proceeds from Lines of Credit			869
Repayments of Lines of Credit			763
Borrowings outstanding	[2]	148	148
Letters of credit issued		0	0
Available for borrowing	[3]	$ 1,102	$ 1,102
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		1.25%

[1] The weighted average interest rate was 1.3% and 6.0% as of June 30, 2019 and December 31, 2018, respectively.

[2] The Company borrowed $869 million and repaid $763 million under its senior unsecured revolving credit facility during the six months ended June 30, 2019.

[3] The margin for borrowings under the senior unsecured revolving credit facility was 1.25% above LIBOR or EURIBOR at current Company credit ratings.