Accumulated Other Comprehensive Income/(Loss) - Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			$ 256,515
Cumulative effect of changes in accounting principles						$ 88
Net change	$ 1,672	$ (75)	2,621	$ (1,107)
Ending balance	263,215	257,458	263,215	257,458
Unrealized gains/(losses) on investment securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	2,616	1,826	1,202	2,164
Cumulative effect of changes in accounting principles						896
Net change	1,093	(227)	2,507	(1,461)
Ending balance	3,709	1,599	3,709	1,599
Translation adjustments, net of hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(751)	(720)	(727)	(470)
Cumulative effect of changes in accounting principles						(277)
Net change	99	88	75	115
Ending balance	(652)	(632)	(652)	(632)
Fair value hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(159)	(94)	(161)	0
Cumulative effect of changes in accounting principles						(54)
Net change	86	(68)	88	(108)
Ending balance	(73)	(162)	(73)	(162)
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	29	19	(109)	76
Cumulative effect of changes in accounting principles						16
Net change	97	(166)	235	(239)
Ending balance	126	(147)	126	(147)
Defined benefit pension and OPEB plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(2,272)	(1,914)	(2,308)	(1,521)
Cumulative effect of changes in accounting principles						(414)
Net change	41	38	77	59
Ending balance	(2,231)	(1,876)	(2,231)	(1,876)
DVA on fair value option elected liabilities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(21)	(180)	596	(368)
Cumulative effect of changes in accounting principles						(79)
Net change	256	260	(361)	527
Ending balance	235	80	235	80
Accumulated other comprehensive income/(loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(558)	(1,063)	(1,507)	(119)
Cumulative effect of changes in accounting principles					$ 0	$ 88
Net change	1,672	(75)	2,621	(1,107)
Ending balance	$ 1,114	$ (1,138)	$ 1,114	$ (1,138)