Total Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jul. 01, 2019	Jan. 01, 2019	Jul. 01, 2018	Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period				$ 81,406
Balance at end of period		$ 83,550	$ 80,074	83,550	$ 80,074
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(865)	(864)	(889)	(767)
Cumulative adjustments for accounting changes									$ (8)
OCI during the period		(96)	(54)	(72)	(143)
Balance at end of period		(961)	(918)	(961)	(918)
AFS Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		108	(1,194)	(930)	(547)
Cumulative adjustments for accounting changes									(111)
OCI during the period		214	(171)	1,252	(707)
Balance at end of period		322	(1,365)	322	(1,365)
Pension, Postretirement and Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(574)	(704)	(578)	(591)
Cumulative adjustments for accounting changes									(124)
OCI during the period		3	5	7	16
Balance at end of period		(571)	(699)	(571)	(699)
DVA
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(720)	(308)	105	(1,155)
Cumulative adjustments for accounting changes									(194)
OCI during the period		332	(709)	(493)	332
Balance at end of period		(388)	(1,017)	(388)	(1,017)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(2,051)	(3,070)	(2,292)	(3,060)
Cumulative adjustments for accounting changes	[1]					$ 0	$ 0	$ 0	$ (437)
OCI during the period		453	(929)	694	(502)
Balance at end of period		$ (1,598)	$ (3,999)	$ (1,598)	$ (3,999)

[1] Cumulative adjustments for accounting changes relate to the adoption of certain accounting updates during the current and prior year periods. See Notes 2 and 14 for further information.