Strategic Lines of Business and Markets (Market Segment Financial Results) (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020		Jun. 30, 2021	Jun. 30, 2020
Net interest income (expense)		$ 465	$ 471		$ 908	$ 984
Provision for credit losses		(135)	138		(317)	549
Noninterest income		284	247		554	484
Noninterest expenses		463	434	[1]	910	851	[1]
Provision (benefit) for income taxes		93	28	[1]	191	9	[1]
Net income		328	118	[1]	678	59	[1]
Net credit-related (recoveries) charge-offs		(11)	50		(8)	134
Assets, average		87,860	81,644		86,218	77,454
Loans, average		49,828	53,498		50,206	51,551
Deposits, average		$ 75,520	$ 64,282		$ 73,467	$ 60,524
Return on average assets	[2]	1.50%	0.58%	[1]	1.59%	0.15%	[1]
Efficiency ratio	[3]	61.66%	60.11%	[1]	62.10%	57.79%	[1]
Michigan [Domain]
Net interest income (expense)		$ 178	$ 161		$ 333	$ 324
Provision for credit losses		(26)	41		(54)	65
Noninterest income		72	64		138	136
Noninterest expenses		136	138	[1]	272	275	[1]
Provision (benefit) for income taxes		29	8	[1]	51	24	[1]
Net income		111	38	[1]	202	96	[1]
Net credit-related (recoveries) charge-offs		1	1		1	4
Assets, average		12,830	13,617		12,851	13,223
Loans, average		12,245	13,092		12,279	12,665
Deposits, average		$ 26,709	$ 23,396		$ 26,191	$ 22,037
Return on average assets	[2]	1.62%	0.62%	[1]	1.51%	0.84%	[1]
Efficiency ratio	[3]	54.18%	61.00%	[1]	57.50%	59.41%	[1]
California [Domain]
Net interest income (expense)		$ 174	$ 169		$ 346	$ 345
Provision for credit losses		(24)	47		(78)	93
Noninterest income		41	34		89	67
Noninterest expenses		116	98	[1]	220	191	[1]
Provision (benefit) for income taxes		29	13	[1]	69	30	[1]
Net income		94	45	[1]	224	98	[1]
Net credit-related (recoveries) charge-offs		0	(1)		1	7
Assets, average		17,679	18,403		17,851	18,164
Loans, average		17,515	18,249		17,702	17,978
Deposits, average		$ 20,582	$ 17,410		$ 20,221	$ 16,985
Return on average assets	[2]	1.75%	0.98%	[1]	2.13%	1.09%	[1]
Efficiency ratio	[3]	53.63%	48.08%	[1]	50.33%	46.32%	[1]
Texas [Domain]
Net interest income (expense)		$ 114	$ 115		$ 227	$ 230
Provision for credit losses		(77)	31		(163)	321
Noninterest income		35	30		71	60
Noninterest expenses		91	89	[1]	179	172	[1]
Provision (benefit) for income taxes		29	5	[1]	60	(45)	[1]
Net income		106	20	[1]	222	(158)	[1]
Net credit-related (recoveries) charge-offs		(12)	46		(10)	116
Assets, average		10,615	11,555		10,627	11,340
Loans, average		10,008	11,162		10,078	10,858
Deposits, average		$ 11,153	$ 10,198		$ 10,965	$ 9,697
Return on average assets	[2]	3.35%	0.71%	[1]	3.61%	(2.79%)	[1]
Efficiency ratio	[3]	61.35%	61.06%	[1]	60.13%	59.24%	[1]
Other Markets
Net interest income (expense)		$ 124	$ 117		$ 241	$ 209
Provision for credit losses		(7)	19		(22)	70
Noninterest income		120	106		224	196
Noninterest expenses		111	104	[1]	223	198	[1]
Provision (benefit) for income taxes		34	21	[1]	64	26	[1]
Net income		106	79	[1]	200	111	[1]
Net credit-related (recoveries) charge-offs		0	4		0	7
Assets, average		11,614	12,345		11,576	11,331
Loans, average		10,048	10,998		10,139	10,051
Deposits, average		$ 15,914	$ 12,178		$ 14,938	$ 10,596
Return on average assets	[2]	2.51%	2.40%	[1]	2.53%	1.92%	[1]
Efficiency ratio	[3]	45.41%	46.21%	[1]	47.92%	48.65%	[1]
Finance & Other
Net interest income (expense)		$ (125)	$ (91)		$ (239)	$ (124)
Provision for credit losses		(1)	0		0	0
Noninterest income		16	13		32	25
Noninterest expenses		9	5	[1]	16	15	[1]
Provision (benefit) for income taxes		(28)	(19)	[1]	(53)	(26)	[1]
Net income		(89)	(64)	[1]	(170)	(88)	[1]
Net credit-related (recoveries) charge-offs		0	0		0	0
Assets, average		35,122	25,724		33,313	23,396
Loans, average		12	(3)		8	(1)
Deposits, average		$ 1,162	$ 1,100		$ 1,152	$ 1,209

[1] See Defined Benefit Pension and Other Postretirement Costs in Note 1.

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

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