Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
		Mar. 31, 2019	Jun. 30, 2019	Jun. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 24,737	$ 24,737	$ 22,270
Other comprehensive income (loss) before reclassifications			568	(507)
Reclassification of certain tax effects			(84)
Amounts reclassified into (out of) earnings			(2)	28
Other comprehensive income (loss)			482	(479)
Ending balance		25,038	25,454	22,521
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(1,356)	(1,356)	(1,009)
Reclassification of certain tax effects	[1]	(84)
Ending balance		(1,180)	(874)	(1,488)
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(89)	(89)	(56)
Other comprehensive income (loss) before reclassifications			18	(68)
Reclassification of certain tax effects			(6)
Amounts reclassified into (out of) earnings			7	11
Other comprehensive income (loss)			19	(57)
Ending balance			(70)	(113)
Net Unrealized Gains (Losses) on Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(175)	(175)	103
Other comprehensive income (loss) before reclassifications			532	(254)
Reclassification of certain tax effects			21
Amounts reclassified into (out of) earnings			0	6
Other comprehensive income (loss)			553	(248)
Ending balance			378	(145)
Net Unrealized Losses on Hedges of Net Investments in Non-U.S. Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		16	16	(65)
Other comprehensive income (loss) before reclassifications			21	35
Reclassification of certain tax effects			(3)
Amounts reclassified into (out of) earnings			0	0
Other comprehensive income (loss)			18	35
Ending balance			34	(30)
Other-Than-Temporary Impairment on Held-to-Maturity Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(2)	(2)	(6)
Other comprehensive income (loss) before reclassifications			2	1
Reclassification of certain tax effects			(1)
Amounts reclassified into (out of) earnings			(1)	(2)
Other comprehensive income (loss)			0	(1)
Ending balance			(2)	(7)
Net Unrealized Losses on Retirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(143)	(143)	(170)
Other comprehensive income (loss) before reclassifications			0	1
Reclassification of certain tax effects			(28)
Amounts reclassified into (out of) earnings			(8)	13
Other comprehensive income (loss)			(36)	14
Ending balance			(179)	(156)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ (963)	(963)	(815)
Other comprehensive income (loss) before reclassifications			(5)	(222)
Reclassification of certain tax effects			(67)
Amounts reclassified into (out of) earnings			0	0
Other comprehensive income (loss)			(72)	(222)
Ending balance			$ (1,035)	$ (1,037)

[1] ⁽¹⁾ Represents the reclassification from accumulated other comprehensive income into retained earnings as a result of our adoption of ASU 2018-02 - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income in the first quarter of 2019.