Equity (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Beginning Balance		$ (1,721)	$ (1,486)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax, Beginning Balance		(300)	(333)
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax, Beginning Balance		(50)	(57)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance		(2,071)	(1,876)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(240)	(278)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		86	64
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax		(10)	(182)	$ 634
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		(223)	26	38
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		6	5	247
Other Comprehensive Income (Loss), Net of Tax		(227)	(151)	919
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Ending Balance		(1,721)	(1,721)	(1,486)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax, Ending Balance		(470)	(300)	(333)
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax, Ending Balance		(38)	(50)	(57)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance		(2,229)	(2,071)	(1,876)
Available-for-Sale securities, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(23)	(214)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		23	(21)
Derivative gains (losses), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(202)	(64)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		36	78
Unfunded pension obligations, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(15)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		27	7
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax		0	(235)	661
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		(166)	14	23
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		12	7	229
Other Comprehensive Income (Loss), Net of Tax		(154)	(214)	913
Cumulative effect of a change in accounting principle (1)	[1]			$ 0	$ (4)	$ 19
ASC 606 Impact [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Beginning Balance		0
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Ending Balance			0
ASC 606 Impact [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance		17
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			19
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance			17
ASC 606 Impact [Member] | Derivative gains (losses), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			19
ASC 606 Impact [Member] | Unfunded pension obligations, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax, Beginning Balance		0
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax, Ending Balance			$ 0
Accounting Standards Update 2017-12 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(4)
Accounting Standards Update 2017-12 [Member] | Available-for-Sale securities, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		0
Accounting Standards Update 2017-12 [Member] | Derivative gains (losses), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		$ (4)

[1] See Note 1—General and Summary of Significant Accounting Policies for further information