Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Mar. 31, 2019	Sep. 30, 2019	Sep. 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			455	(734)
Reclassification of certain tax effects			(84)
Amounts reclassified into (out of) earnings			0	32
Other comprehensive income (loss)			371	(702)
Ending balance		25,038	25,209	24,502
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)	(985)	(1,711)
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			22	(42)
Reclassification of certain tax effects			(6)
Amounts reclassified into (out of) earnings			10	15
Other comprehensive income (loss)			26	(27)
Ending balance			(63)	(83)
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			678	(452)
Reclassification of certain tax effects			21
Amounts reclassified into (out of) earnings			0	6
Other comprehensive income (loss)			699	(446)
Ending balance			524	(343)
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			78	54
Reclassification of certain tax effects			(3)
Amounts reclassified into (out of) earnings			0	0
Other comprehensive income (loss)			75	54
Ending balance			91	(11)
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			3	4
Reclassification of certain tax effects			(1)
Amounts reclassified into (out of) earnings			(1)	(3)
Other comprehensive income (loss)			1	1
Ending balance			(1)	(5)
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	0
Reclassification of certain tax effects			(28)
Amounts reclassified into (out of) earnings			(9)	14
Other comprehensive income (loss)			(37)	14
Ending balance			(180)	(156)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ (963)	(963)	(815)
Other comprehensive income (loss) before reclassifications			(326)	(298)
Reclassification of certain tax effects			(67)
Amounts reclassified into (out of) earnings			0	0
Other comprehensive income (loss)			(393)	(298)
Ending balance			$ (1,356)	$ (1,113)

[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.