Schedule I - Condensed Financial Information of Parent (Statement of Comprehensive Income Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Foreign currency translation adjustments, income tax benefit (expense)	$ 17	$ 1	$ 1
Foreign currency, reclassification to earnings, income tax benefit (expense)	0	0	0
Change in derivative fair value, income tax benefit (expense)	10	(7)	16
Derivative reclassification to earnings, income tax benefit (expense)	(1)	(8)	(11)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Tax	1	6	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax	6	106	(29)
Pension, amortization of net actuarial loss, income tax benefit (expense)	(135)	(3)	(9)
Parent Company
Condensed Financial Statements, Captions [Line Items]
Foreign currency translation adjustments, income tax benefit (expense)	11	1	1
Foreign currency, reclassification to earnings, income tax benefit (expense)	0	0	0
Change in derivative fair value, income tax benefit (expense)	13	(5)	4
Derivative reclassification to earnings, income tax benefit (expense)	1	1	(12)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Tax	(1)	(5)	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax	6	10	(7)
Pension, amortization of net actuarial loss, income tax benefit (expense)	$ (126)	$ 2	$ (2)