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 [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 41	$ 47	$ 19
Charged to Costs & Expenses	10	9	32
Charged to Other Accounts	0	0	0
Deductions	14	15	4
Balance at End of Period	37	41	47
Deferred Tax Asset Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	445	346	294
Charged to Costs & Expenses	0	0	0
Charged to Other Accounts	0	99	52
Deductions	30	0	0
Balance at End of Period	$ 415	$ 445	$ 346