Stockholders' Equity (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net current period other comprehensive income (loss)		$ (4)	$ (381)	$ 22	$ (264)
Net current period other comprehensive income (loss)		26	79	22	79
Defined Benefit Pension Plans
Defined benefit and other postretirement benefit plans - Beginning balance				(1,017)	(976)
Other comprehensive income/(loss) before reclassifications				1	27
(Income)/loss reclassified from AOCI	[1]			6	39
Net current period other comprehensive income (loss)				7	66
Defined benefit and other postretirement benefit plans - Ending balance		(1,010)	(1,035)	(1,010)	(1,035)
Other Postretirement Benefit Plans
Defined benefit and other postretirement benefit plans - Beginning balance				12	(39)
Other comprehensive income/(loss) before reclassifications				15	13
(Income)/loss reclassified from AOCI	[1]			(1)	(1)
Net current period other comprehensive income (loss)				14	12
Defined benefit and other postretirement benefit plans - Ending balance		26	(32)	26	(32)
Unrealized Translation
Unrealized translation - Beginning balance				(2,297)	(1,864)
Other comprehensive income/(loss) before reclassifications				29	(254)
(Income)/loss reclassified from AOCI				0	1
Net current period other comprehensive income (loss)				29	(253)
Unrealized translation - Ending balance		(2,268)	(2,135)	(2,268)	(2,135)
Accumulated Foreign Currency Adjustment Attributable to Parent
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle					(18)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent | Defined Benefit Pension Plans
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle					(125)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent | Other Postretirement Benefit Plans
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle					(5)
Cash Flow Hedges and Other
Cash flow hedge and other - Beginning balance				3	(40)
Other comprehensive income/(loss) before reclassifications				(12)	15
(Income)/loss reclassified from AOCI				(8)	13
Net current period other comprehensive income (loss)				(20)	28
Cash flow hedge and other - Ending balance		$ (17)	$ (20)	$ (17)	(20)
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle					$ (8)

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