Debt Debt (Accounts Receivable Securitization Facility) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Debt Instrument [Line Items]
Cash Flows Between Transferor and Transferee, Proceeds from New Transfers		$ 158
Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Line of Credit, Current	[2]	80	[1]	$ 0
Letters of credit issued		29
Available for borrowing		11
Line of Credit Facility, Current Borrowing Capacity		120
Line of Credit Facility, Maximum Borrowing Capacity	[3]	120
Secured Debt [Member] | Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Debt		85
Repayments of Lines of Credit		$ 5

[1] The Company borrowed $85 million and repaid $5 million during the year ended December 31, 2017.

[2] The weighted average interest rate was 2.1% as of December 31, 2017.

[3] Outstanding accounts receivable transferred to the SPE was $158 million.