Stockholders' Equity (Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 5,128	$ 5,728	$ 5,674
Unrealized gain (loss)	(302)	34	39
Unrealized actuarial gain(loss) and prior service credit (cost)	(48)	(15)	(70)
Tax effect	5	50	(37)
Other comprehensive income (loss), net of tax	(345)	69	(68)
Less: Other comprehensive loss available to noncontrolling interests	2	0	0
Other comprehensive income (loss), net of tax	(345)	69	(68)
Ending balance	3,205	5,128	5,728
Foreign Currency
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,320)	(1,395)	(1,348)
Unrealized gain (loss)	(272)	32	(30)
Unrealized actuarial gain(loss) and prior service credit (cost)	0	0	0
Tax effect	(15)	43	(17)
Other comprehensive income (loss), net of tax	(287)	75	(47)
Less: Other comprehensive loss available to noncontrolling interests	2	0	0
Other comprehensive income (loss), net of tax	(289)	75	(47)
Ending balance	(1,588)	(1,320)	(1,395)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	11	15	(30)
Unrealized gain (loss)	(30)	(4)	71
Unrealized actuarial gain(loss) and prior service credit (cost)	0	0	0
Tax effect	7	0	(26)
Other comprehensive income (loss), net of tax	(23)	(4)	45
Less: Other comprehensive loss available to noncontrolling interests	0	0	0
Other comprehensive income (loss), net of tax	(23)	(4)	45
Ending balance	(33)	11	15
Pension and Postretirement Liability
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,039)	(1,031)	(967)
Unrealized gain (loss)	0	0	0
Unrealized actuarial gain(loss) and prior service credit (cost)	(48)	(15)	(70)
Tax effect	13	7	6
Other comprehensive income (loss), net of tax	(35)	(8)	(64)
Less: Other comprehensive loss available to noncontrolling interests	0	0	0
Other comprehensive income (loss), net of tax	(35)	(8)	(64)
Ending balance	(1,074)	(1,039)	(1,031)
Marketable Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	17	11	13
Unrealized gain (loss)	0	6	(2)
Unrealized actuarial gain(loss) and prior service credit (cost)	0	0	0
Tax effect	0	0	0
Other comprehensive income (loss), net of tax	0	6	(2)
Less: Other comprehensive loss available to noncontrolling interests	0	0	0
Other comprehensive income (loss), net of tax	0	6	(2)
Ending balance	0	17	11
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(2,331)	(2,400)	(2,332)
Other comprehensive income (loss), net of tax	(347)	69	(68)
Ending balance	$ (2,695)	$ (2,331)	$ (2,400)
Adjustment to beginning accumulated other comprehensive loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption				$ (17)
Adjustment to beginning accumulated other comprehensive loss | Foreign Currency
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption				21
Adjustment to beginning accumulated other comprehensive loss | Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption				(21)
Adjustment to beginning accumulated other comprehensive loss | Pension and Postretirement Liability
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption				0
Adjustment to beginning accumulated other comprehensive loss | Marketable Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption				(17)
Adjustment to beginning accumulated other comprehensive loss | Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption				$ (17)