Stockholders' Equity (Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 5,728	$ 5,674	$ 5,796
Unrealized actuarial gain(loss) and prior service credit (cost)	(15)	(70)	(79)
Tax effect	50	(37)	30
Other comprehensive income (loss), net of tax	69	(68)	(501)
Ending balance	5,128	5,728	5,674
Foreign Currency
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,395)	(1,348)	(925)
Unrealized gain (loss)	32	(30)	(432)
Unrealized actuarial gain(loss) and prior service credit (cost)	0	0	0
Tax effect	43	(17)	0
Other comprehensive income (loss), net of tax	75	(47)	(432)
Less: Other comprehensive loss available to noncontrolling interests	0	0	(9)
Other comprehensive income (loss), net of tax	75	(47)	(423)
Ending balance	(1,320)	(1,395)	(1,348)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	15	(30)	(7)
Unrealized gain (loss)	(4)	71	(23)
Unrealized actuarial gain(loss) and prior service credit (cost)	0	0	0
Tax effect	0	(26)	0
Other comprehensive income (loss), net of tax	(4)	45	(23)
Less: Other comprehensive loss available to noncontrolling interests	0	0	0
Other comprehensive income (loss), net of tax	(4)	45	(23)
Ending balance	11	15	(30)
Pension and Postretirement Liability
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,031)	(967)	(918)
Unrealized gain (loss)	0	0	0
Unrealized actuarial gain(loss) and prior service credit (cost)	(15)	(70)	(79)
Tax effect	7	6	30
Other comprehensive income (loss), net of tax	(8)	(64)	(49)
Less: Other comprehensive loss available to noncontrolling interests	0	0	0
Other comprehensive income (loss), net of tax	(8)	(64)	(49)
Ending balance	(1,039)	(1,031)	(967)
Marketable Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	11	13	10
Unrealized gain (loss)	6	(2)	3
Unrealized actuarial gain(loss) and prior service credit (cost)	0	0	0
Tax effect	0	0	0
Other comprehensive income (loss), net of tax	6	(2)	3
Less: Other comprehensive loss available to noncontrolling interests	0	0	0
Other comprehensive income (loss), net of tax	6	(2)	3
Ending balance	17	11	13
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(2,400)	(2,332)	(1,840)
Unrealized gain (loss)	34	39	(452)
Unrealized actuarial gain(loss) and prior service credit (cost)	(15)	(70)	(79)
Tax effect	50	(37)	30
Other comprehensive income (loss), net of tax	69	(68)	(501)
Less: Other comprehensive loss available to noncontrolling interests	0	0	(9)
Other comprehensive income (loss), net of tax	69	(68)	(492)
Ending balance	$ (2,331)	$ (2,400)	$ (2,332)