Debt (Schedule of Balances Available for Borrowing) (Details) - USD ($) $ in Millions					12 Months Ended
		Dec. 31, 2017		Sep. 26, 2016	Dec. 31, 2017		Dec. 31, 2016
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowings outstanding	[2]	$ 97	[1]		$ 97	[1]	$ 0
Letters of credit issued		0			0
Available for borrowing	[3]	$ 903			903
Revolving Credit Facility [Member] | Senior Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Proceeds from Lines of Credit					528
Repayments of Lines of Credit				$ 411	$ 431
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		1.50%

[1] The Company borrowed $528 million and repaid $431 million under its senior unsecured revolving credit facility during the year ended December 31, 2017

[2] The weighted average interest rate was 4.1% as of December 31, 2017.

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