Debt (Schedule of Balances Available for Borrowing) (Details) - USD ($) $ in Millions					12 Months Ended
		Dec. 31, 2019		May 08, 2019	Dec. 31, 2019		Dec. 31, 2018
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowings outstanding	[1]	$ 272	[2]		$ 272	[2]	$ 40
Letters of credit issued		0			0
Available for borrowing	[3]	$ 978			978
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Repayments of Lines of Credit				$ 156
Revolving Credit Facility [Member] | Senior Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Proceeds from Lines of Credit					1,300
Repayments of Lines of Credit					$ 1,100
London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member] | Senior Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.25%

[1] The weighted average interest rate was 1.6% and 6.0% as of December 31, 2019 and 2018, respectively.

[2] The Company borrowed $1.3 billion and repaid $1.1 billion under its senior unsecured revolving credit facility during the year ended December 31, 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.