Stockholders' Equity (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Net current period other comprehensive income (loss)		$ 117	$ 267
Net current period other comprehensive income (loss)		0	(2)
Defined Benefit Pension Plans
Defined benefit and other postretirement benefit plans - Beginning balance		(976)	(1,097)
Other comprehensive income/(loss) before reclassifications		(10)	(11)
(Income)/loss reclassified from AOCI	[1]	10	9
Net current period other comprehensive income (loss)		0	(2)
Defined benefit and other postretirement benefit plans - Ending balance		(976)	(1,099)
Other Postretirement Benefit Plans
Defined benefit and other postretirement benefit plans - Beginning balance		(39)	(31)
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		(39)	(31)
Cash Flow Hedges and Other
Cash flow hedge and other - Beginning balance		(40)	5
Other comprehensive income/(loss) before reclassifications		(9)	(15)
(Income)/loss reclassified from AOCI		8	(1)
Net current period other comprehensive income (loss)		(1)	(16)
Cash flow hedge and other - Ending balance		(41)	(11)
Unrealized Translation
Unrealized translation - Beginning balance		(1,864)	(2,351)
Other comprehensive income/(loss) before reclassifications		116	248
(Income)/loss reclassified from AOCI		0	0
Net current period other comprehensive income (loss)		116	248
Unrealized translation - Ending balance		$ (1,748)	$ (2,103)

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