Strategic Lines of Business and Markets (Market Segment Financial Results) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net interest income (expense)		$ 469	$ 458	$ 471	$ 513	$ 544	$ 586	$ 603	$ 606	$ 1,911	$ 2,339	$ 2,352
Provision for credit losses		(17)	5	138	411	8	35	44	(13)	537	74	(1)
Noninterest income										1,001	1,010	976
Noninterest expenses		473	446	440	425	451	435	424	433	1,784	1,743	1,794
Provision (benefit) for income taxes		(63)	(48)	(27)	21	(82)	(80)	(87)	(85)	(117)	(334)	(300)
Net Income		$ 215	$ 211	$ 113	$ (65)	$ 269	$ 292	$ 298	$ 339	474	1,198	1,235
Net loan charge-offs (recoveries)										196	107	51
Assets, average										81,146	71,488	70,724
Loans, average										51,631	50,511	48,766
Deposits, average										$ 65,038	$ 55,481	$ 55,935
Return on average assets	[1]									0.58%	1.68%	1.75%
Efficiency ratio	[2]									61.15%	51.82%	53.56%
Michigan [Domain]
Net interest income (expense)										$ 660	$ 729	$ 727
Provision for credit losses										95	(11)	30
Noninterest income										273	291	296
Noninterest expenses										559	554	577
Provision (benefit) for income taxes										(54)	(108)	(90)
Net Income										225	369	326
Net loan charge-offs (recoveries)										14	11	7
Assets, average										13,179	13,149	13,202
Loans, average										12,509	12,553	12,531
Deposits, average										$ 23,500	$ 20,081	$ 20,770
Return on average assets	[1]									0.92%	1.77%	1.52%
Efficiency ratio	[2]									59.76%	54.01%	56.21%
California [Domain]
Net interest income (expense)										$ 723	$ 808	$ 786
Provision for credit losses										134	(33)	26
Noninterest income										147	173	164
Noninterest expenses										414	406	424
Provision (benefit) for income taxes										(75)	(154)	(123)
Net Income										247	454	377
Net loan charge-offs (recoveries)										31	8	27
Assets, average										18,562	18,731	18,422
Loans, average										18,265	18,413	18,161
Deposits, average										$ 19,386	$ 16,846	$ 16,951
Return on average assets	[1]									1.21%	2.42%	2.05%
Efficiency ratio	[2]									47.58%	41.28%	44.64%
Texas [Domain]
Net interest income (expense)										$ 465	$ 493	$ 474
Provision for credit losses										270	119	(53)
Noninterest income										120	128	130
Noninterest expenses										359	345	365
Provision (benefit) for income taxes										11	(38)	(64)
Net Income										(33)	119	228
Net loan charge-offs (recoveries)										151	93	12
Assets, average										11,287	11,269	10,380
Loans, average										10,813	10,616	9,812
Deposits, average										$ 10,209	$ 8,780	$ 8,991
Return on average assets	[1]									(0.28%)	1.06%	2.20%
Efficiency ratio	[2]									61.28%	55.59%	60.30%
Other Markets
Net interest income (expense)										$ 429	$ 376	$ 355
Provision for credit losses										38	(5)	(1)
Noninterest income										388	365	359
Noninterest expenses										414	370	376
Provision (benefit) for income taxes										(79)	(74)	(60)
Net Income										286	302	279
Net loan charge-offs (recoveries)										0	(5)	5
Assets, average										11,020	9,732	9,049
Loans, average										10,052	8,934	8,273
Deposits, average										$ 10,742	$ 7,916	$ 8,157
Return on average assets	[1]									2.45%	3.10%	3.08%
Efficiency ratio	[2]									50.66%	49.90%	52.82%
Finance & Other
Net interest income (expense)										$ (366)	$ (67)	$ 10
Provision for credit losses										0	4	(3)
Noninterest income										73	53	27
Noninterest expenses										38	68	52
Provision (benefit) for income taxes										80	40	37
Net Income										(251)	(46)	25
Net loan charge-offs (recoveries)										0	0	0
Assets, average										27,098	18,607	19,671
Loans, average										(8)	(5)	(11)
Deposits, average										$ 1,201	$ 1,858	$ 1,066

[1] Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity.

[2] Noninterest expenses as a percentage of the sum of net interest income and noninterest income excluding net gains (losses) from securities and a derivative contract tied to the conversion rate of Visa Class B shares.