Stockholders' Equity (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Net current period other comprehensive income (loss)		$ 26	$ 117
Net current period other comprehensive income (loss)		(4)	0
Defined Benefit Pension Plans
Defined benefit and other postretirement benefit plans - Beginning balance		(1,017)	(976)
Other comprehensive income/(loss) before reclassifications		(7)	(10)
(Income)/loss reclassified from AOCI	[1]	3	10
Net current period other comprehensive income (loss)		(4)	0
Defined benefit and other postretirement benefit plans - Ending balance		(1,021)	(976)
Other Postretirement Benefit Plans
Defined benefit and other postretirement benefit plans - Beginning balance		12	(39)
Other comprehensive income/(loss) before reclassifications		0	0
(Income)/loss reclassified from AOCI	[1]	0	0
Net current period other comprehensive income (loss)		0	0
Defined benefit and other postretirement benefit plans - Ending balance		12	(39)
Cash Flow Hedges and Other
Cash flow hedge and other - Beginning balance		3	(40)
Other comprehensive income/(loss) before reclassifications		(12)	(9)
(Income)/loss reclassified from AOCI		(5)	8
Net current period other comprehensive income (loss)		(17)	(1)
Cash flow hedge and other - Ending balance		(14)	(41)
Unrealized Translation
Unrealized translation - Beginning balance		(2,297)	(1,864)
Other comprehensive income/(loss) before reclassifications		31	116
(Income)/loss reclassified from AOCI		0	0
Net current period other comprehensive income (loss)		31	116
Unrealized translation - Ending balance		$ (2,266)	$ (1,748)

[1] Included in computation of net periodic benefit costs.