Stockholders' Equity - Reclassifications from AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	$ 6,156	$ 5,555	$ 17,721	$ 17,040
Interest expense	382	660	1,217	2,602
Non-interest income	243	706	592	1,017
Income from continuing operations before income taxes	3,986	3,502	12,750	139
Income tax provision	882	1,096	2,782	(10)
Net income (loss)	3,104	2,406	9,965	148
Accumulated other comprehensive income	1,360		1,360			$ 3,494
Other comprehensive income (loss), net of tax	(432)	(148)	(2,134)	2,685
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	256	101	747	305
Securities available for sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income	881	2,374	881	2,374	$ 1,089	2,186	$ 2,373	$ 935
Other comprehensive income (loss) before reclassifications	(206)	20	(1,300)	1,466
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2)	(19)	(5)	(19)
Other comprehensive income (loss), net of tax	(208)	1	(1,305)	1,447
Securities available for sale | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-interest income	2	25	6	25
Income tax provision	0	6	1	6
Net income (loss)	2	19	5	19
Hedging Relationships
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income	535	1,610	535	1,610	730	1,362	1,785	354
Other comprehensive income (loss) before reclassifications	57	(95)	(88)	1,540
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(252)	(80)	(739)	(284)
Other comprehensive income (loss), net of tax	(195)	(175)	(827)	1,256
Hedging Relationships | Interest rate contracts | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	250	179	730	347
Hedging Relationships | Foreign exchange contracts | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	0	1	1	10
Interest expense	0	(1)	(2)	(3)
Non-interest income	83	(73)	245	20
Income from continuing operations before income taxes	333	106	974	374
Income tax provision	81	26	235	90
Net income (loss)	252	80	739	284
Foreign Currency Translation Adjustments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income	(30)	(123)	(30)	(123)	(3)	(31)	(151)	(107)
Other comprehensive income (loss) before reclassifications	(27)	28	1	(16)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	0	0
Other comprehensive income (loss), net of tax	(27)	28	1	(16)
Other
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income	(26)	(28)	(26)	(28)	(24)	(23)	(26)	(26)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2)	(2)	(3)	(2)
Other comprehensive income (loss), net of tax	(2)	(2)	(3)	(2)
Other | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income from continuing operations before income taxes	3	2	4	2
Income tax provision	1	0	1	0
Net income (loss)	2	2	3	2
Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income	1,360	3,833	1,360	3,833	$ 1,792	$ 3,494	$ 3,981	$ 1,156
Other comprehensive income (loss) before reclassifications	(176)	(47)	(1,387)	2,990
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(256)	(101)	(747)	(305)
Other comprehensive income (loss), net of tax	$ (432)	$ (148)	$ (2,134)	$ 2,685