Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ (2,597)
Pension and other postretirement benefits	$ 3	$ 1	(24)	$ 29
Balance as of end of period	(2,606)		(2,606)
Tax impact for the changes in each component of accumulated other comprehensive (loss) income
Investment securities	9	(2)	13	(5)
Foreign currency translation adjustments	1	(70)	15	(68)
Net investment hedges	28	107	(22)	53
Pension and other postretirement benefits	4	6	(7)	9
Total tax impact	42	41	(1)	(11)
Accumulated Other Comprehensive (Loss) Income [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,599)	(2,381)	(2,597)	(2,428)
Net unrealized gains	26	(7)	43	(20)
Net translation of investments in foreign operations	(123)	(416)	47	(224)
Net gains (losses) related to hedges of investment in foreign operations	87	320	(75)	158
Pension and other postretirement benefits	3	1	(24)	29
Other				2
Net change in accumulated other comprehensive income (loss)	(7)	(102)	(9)	(55)
Balance as of end of period	(2,606)	(2,483)	(2,606)	(2,483)
Net Unrealized Gains (Losses) on Investment Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	9	(11)	(8)	0
Net unrealized gains	26	(7)	43	(20)
Net translation of investments in foreign operations	0	0	0	0
Net gains (losses) related to hedges of investment in foreign operations	0	0	0	0
Pension and other postretirement benefits	0	0	0	0
Other				2
Net change in accumulated other comprehensive income (loss)	26	(7)	43	(18)
Balance as of end of period	35	(18)	35	(18)
Foreign Currency Translation Adjustments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,125)	(1,931)	(2,133)	(1,961)
Net unrealized gains	0	0	0	0
Net translation of investments in foreign operations	(123)	(416)	47	(224)
Net gains (losses) related to hedges of investment in foreign operations	87	320	(75)	158
Pension and other postretirement benefits	0	0	0	0
Other				0
Net change in accumulated other comprehensive income (loss)	(36)	(96)	(28)	(66)
Balance as of end of period	(2,161)	(2,027)	(2,161)	(2,027)
Net Unrealized Pension and Other Postretirement Gains (Losses) [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(483)	(439)	(456)	(467)
Net unrealized gains	0	0	0	0
Net translation of investments in foreign operations	0	0	0	0
Net gains (losses) related to hedges of investment in foreign operations	0	0	0	0
Pension and other postretirement benefits	3	1	(24)	29
Other				0
Net change in accumulated other comprehensive income (loss)	3	1	(24)	29
Balance as of end of period	$ (480)	$ (438)	$ (480)	$ (438)