Stockholders' Equity (Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018	Jan. 01, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 3,205	$ 5,128	$ 5,728
Unrealized gain (loss)	37	(302)	34
Unrealized actuarial gain(loss) and prior service credit (cost)	52	(48)	(15)
Tax effect	(12)	5	50
Other comprehensive income (loss), net of tax	77	(345)	69
Less: Other comprehensive loss available to noncontrolling interests	0	2	0
Other comprehensive income (loss), net of tax	77	(345)	69
Ending balance	4,118	3,205	5,128
Foreign Currency
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,588)	(1,320)	(1,395)
Unrealized gain (loss)	54	(272)	32
Unrealized actuarial gain(loss) and prior service credit (cost)	0	0	0
Tax effect	2	(15)	43
Other comprehensive income (loss), net of tax	56	(287)	75
Less: Other comprehensive loss available to noncontrolling interests	0	2	0
Other comprehensive income (loss), net of tax	56	(289)	75
Ending balance	(1,532)	(1,588)	(1,320)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(33)	11	15
Unrealized gain (loss)	(17)	(30)	(4)
Unrealized actuarial gain(loss) and prior service credit (cost)	0	0	0
Tax effect	4	7	0
Other comprehensive income (loss), net of tax	(13)	(23)	(4)
Less: Other comprehensive loss available to noncontrolling interests	0	0	0
Other comprehensive income (loss), net of tax	(13)	(23)	(4)
Ending balance	(46)	(33)	11
Pension and Postretirement Liability
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,074)	(1,039)	(1,031)
Unrealized gain (loss)	0	0	0
Unrealized actuarial gain(loss) and prior service credit (cost)	52	(48)	(15)
Tax effect	(18)	13	7
Other comprehensive income (loss), net of tax	34	(35)	(8)
Less: Other comprehensive loss available to noncontrolling interests	0	0	0
Other comprehensive income (loss), net of tax	34	(35)	(8)
Ending balance	(1,040)	(1,074)	(1,039)
Marketable Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0	17	11
Unrealized gain (loss)	0	0	6
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	0	6
Less: Other comprehensive loss available to noncontrolling interests	0	0	0
Other comprehensive income (loss), net of tax	0	0	6
Ending balance	0	0	17
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(2,695)	(2,331)	(2,400)
Other comprehensive income (loss), net of tax	77	(347)	69
Ending balance	$ (2,618)	$ (2,695)	$ (2,331)
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)	$ (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)