Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts, Current [Member]
Valuation Allowance [Line Items]
Beginning Balance	$ 8	$ 10	$ 11
Additions	5	4	4
Net Deductions and Other	4	6	5
Ending Balance	9	8	10
Valuation Allowance of Deferred Tax Assets [Member]
Valuation Allowance [Line Items]
Beginning Balance	1,209	1,201	1,127
Additions	140	176	182
Net Deductions and Other	493	168	108
Ending Balance	$ 856	$ 1,209	$ 1,201