Stockholders' Equity (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net current period other comprehensive income (loss)		$ (79)	$ 128	$ (343)	$ 450
Net current period other comprehensive income (loss)		22	(8)	101	(11)
Defined Benefit Pension Plans
Defined benefit and other postretirement benefit plans - Beginning balance				(976)	(1,097)
Other comprehensive income/(loss) before reclassifications				25	(34)
(Income)/loss reclassified from AOCI	[1]			63	27
Net current period other comprehensive income (loss)				88	(7)
Tax effects reclassified from AOCI				(125)
Defined benefit and other postretirement benefit plans - Ending balance		(1,013)	(1,104)	(1,013)	(1,104)
Other Postretirement Benefit Plans
Defined benefit and other postretirement benefit plans - Beginning balance				(39)	(31)
Other comprehensive income/(loss) before reclassifications				14	(3)
(Income)/loss reclassified from AOCI	[1]			(1)	(1)
Net current period other comprehensive income (loss)				13	(4)
Tax effects reclassified from AOCI				(5)
Defined benefit and other postretirement benefit plans - Ending balance		(31)	(35)	(31)	(35)
Cash Flow Hedges and Other
Cash flow hedge and other - Beginning balance				(40)	5
Other comprehensive income/(loss) before reclassifications				17	(55)
(Income)/loss reclassified from AOCI				14	6
Net current period other comprehensive income (loss)				31	(49)
Tax effects reclassified from AOCI				(8)
Cash flow hedge and other - Ending balance		(17)	(44)	(17)	(44)
Unrealized Translation
Unrealized translation - Beginning balance				(1,864)	(2,351)
Other comprehensive income/(loss) before reclassifications				(333)	439
(Income)/loss reclassified from AOCI				1	0
Net current period other comprehensive income (loss)				(332)	439
Tax effects reclassified from AOCI				(18)
Unrealized translation - Ending balance		$ (2,214)	$ (1,912)	$ (2,214)	$ (1,912)

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