Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 4,636	$ 4,636	$ 3,945	$ 1,742
Other comprehensive loss		(141)	(25)	(530)
Ending balance		5,097	4,636	3,945
Currency translation adjustment reclassification from AOCI tax impact	0
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,586)	(2,586)	(2,561)	(2,031)
Other comprehensive income (loss) before reclassifications		(344)	(52)	(350)
Net losses (gains) reclassified from accumulated other comprehensive loss		203	27	(180)
Other comprehensive loss		(141)	(25)	(530)
Ending balance		(2,727)	(2,586)	(2,561)
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,435)	(1,435)	(1,270)	(603)
Other comprehensive income (loss) before reclassifications		680	(165)	(667)
Net losses (gains) reclassified from accumulated other comprehensive loss		316
Other comprehensive loss		996	(165)	(667)
Ending balance		(439)	(1,435)	(1,270)
Net investment hedging activities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	140	140	0	0
Other comprehensive income (loss) before reclassifications		(343)	140	0
Other comprehensive loss		(343)	140	0
Ending balance		(203)	140	0
Pension and post- employment benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,513)	(1,513)	(1,378)	(1,608)
Other comprehensive income (loss) before reclassifications		(480)	(194)	147
Net losses (gains) reclassified from accumulated other comprehensive loss		74	59	83
Other comprehensive loss		(406)	(135)	230
Ending balance		(1,919)	(1,513)	(1,378)
Marketable security activities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	46	46	47	3
Other comprehensive income (loss) before reclassifications		29	7	48
Net losses (gains) reclassified from accumulated other comprehensive loss		(75)	(8)	(4)
Other comprehensive loss		(46)	(1)	44
Ending balance		0	46	47
Cash flow hedging activities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 176	176	40	177
Other comprehensive income (loss) before reclassifications		(230)	160	122
Net losses (gains) reclassified from accumulated other comprehensive loss		(112)	(24)	(259)
Other comprehensive loss		(342)	136	(137)
Ending balance		$ (166)	$ 176	$ 40