Business Segment Information (Market Segment Financial Results) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net interest income (expense)		$ 458	$ 586	$ 1,442	$ 1,795
Provision for credit losses		5	35	554	66
Noninterest income		252	256	736	744
Noninterest expenses		446	435	1,311	1,292
Provision (benefit) for income taxes		48	80	54	252
Net income		211	292	259	929
Net credit-related charge-offs (recoveries)		33	42	167	86
Assets, average		84,268	71,736	79,742	70,927
Loans, average		52,013	50,887	51,706	50,514
Deposits, average		$ 68,763	$ 55,716	$ 63,291	$ 54,909
Return on average assets	[1]	0.99%	1.61%	0.43%	1.75%
Efficiency ratio	[2]	62.79%	51.54%	60.10%	50.66%
Michigan
Net interest income (expense)		$ 168	$ 185	$ 490	$ 558
Provision for credit losses		19	(1)	83	(6)
Noninterest income		66	74	202	218
Noninterest expenses		139	139	418	412
Provision (benefit) for income taxes		13	27	36	83
Net income		63	94	155	287
Net credit-related charge-offs (recoveries)		6	6	9	10
Assets, average		13,280	13,205	13,272	13,170
Loans, average		12,607	12,554	12,604	12,605
Deposits, average		$ 24,759	$ 20,164	$ 22,995	$ 19,959
Return on average assets	[1]	0.95%	1.79%	0.86%	1.85%
Efficiency ratio	[2]	59.79%	53.30%	60.20%	53.00%
California
Net interest income (expense)		$ 179	$ 203	$ 537	$ 614
Provision for credit losses		11	(6)	113	(11)
Noninterest income		33	41	105	121
Noninterest expenses		102	102	303	301
Provision (benefit) for income taxes		21	37	51	113
Net income		78	111	175	332
Net credit-related charge-offs (recoveries)		16	5	31	9
Assets, average		18,357	18,595	18,563	18,877
Loans, average		18,095	18,261	18,263	18,572
Deposits, average		$ 20,130	$ 16,705	$ 18,691	$ 16,420
Return on average assets	[1]	1.46%	2.37%	1.18%	2.36%
Efficiency ratio	[2]	47.98%	41.70%	47.16%	40.89%
Texas
Net interest income (expense)		$ 117	$ 125	$ 348	$ 373
Provision for credit losses		(25)	50	296	88
Noninterest income		28	31	88	97
Noninterest expenses		89	86	264	255
Provision (benefit) for income taxes		17	5	(29)	30
Net income		64	15	(95)	97
Net credit-related charge-offs (recoveries)		11	34	127	73
Assets, average		11,365	11,462	11,369	11,240
Loans, average		10,923	10,805	10,889	10,586
Deposits, average		$ 10,654	$ 8,705	$ 10,026	$ 8,690
Return on average assets	[1]	2.14%	0.48%	(1.10%)	1.13%
Efficiency ratio	[2]	61.16%	55.57%	60.41%	54.35%
Other Markets
Net interest income (expense)		$ 118	$ 96	$ 315	$ 281
Provision for credit losses		0	(9)	62	(4)
Noninterest income		100	94	291	272
Noninterest expenses		105	90	300	273
Provision (benefit) for income taxes		24	22	49	57
Net income		89	87	195	227
Net credit-related charge-offs (recoveries)		0	(3)	0	(6)
Assets, average		11,322	10,100	10,943	9,548
Loans, average		10,399	9,282	9,955	8,760
Deposits, average		$ 12,035	$ 7,879	$ 10,378	$ 7,876
Return on average assets	[1]	2.68%	3.45%	2.28%	3.20%
Efficiency ratio	[2]	48.22%	47.08%	49.60%	49.20%
Finance & Other
Net interest income (expense)		$ (124)	$ (23)	$ (248)	$ (31)
Provision for credit losses		0	1	0	(1)
Noninterest income		25	16	50	36
Noninterest expenses		11	18	26	51
Provision (benefit) for income taxes		(27)	(11)	(53)	(31)
Net income		(83)	(15)	(171)	(14)
Net credit-related charge-offs (recoveries)		0	0	0	0
Assets, average		29,944	18,374	25,595	18,092
Loans, average		(11)	(15)	(5)	(9)
Deposits, average		$ 1,185	$ 2,263	$ 1,201	$ 1,964

[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 losses from securities and a derivative contract tied to the conversion rate of Visa Class B shares.