Business Segment Information (Market Segment Financial Results) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Net interest income (expense)		$ 606	$ 549
Provision for credit losses		(13)	12
Noninterest income		238	244
Noninterest expenses		433	446
Provision (benefit) for income taxes		85	54
Net income (loss)		339	281
Net credit-related charge-offs (recoveries)		11	28
Assets, average		69,771	70,326
Loans, average		49,677	48,421
Deposits, average		$ 53,996	$ 56,090
Return on average assets	[1]	1.97%	1.62%
Efficiency ratio	[2]	50.81%	56.33%
Discrete tax benefits		$ 11	$ 22
Michigan
Net interest income (expense)		187	175
Provision for credit losses		5	34
Noninterest income		71	73
Noninterest expenses		140	144
Provision (benefit) for income taxes		26	17
Net income (loss)		87	53
Net credit-related charge-offs (recoveries)		4	(1)
Assets, average		13,075	13,395
Loans, average		12,557	12,604
Deposits, average		$ 19,893	$ 21,224
Return on average assets	[1]	1.74%	0.98%
Efficiency ratio	[2]	53.82%	57.99%
California
Net interest income (expense)		$ 205	$ 188
Provision for credit losses		(1)	(2)
Noninterest income		41	39
Noninterest expenses		100	106
Provision (benefit) for income taxes		37	32
Net income (loss)		110	91
Net credit-related charge-offs (recoveries)		(3)	13
Assets, average		19,048	18,582
Loans, average		18,768	18,347
Deposits, average		$ 16,245	$ 17,091
Return on average assets	[1]	2.32%	1.98%
Efficiency ratio	[2]	40.85%	46.82%
Texas
Net interest income (expense)		$ 122	$ 111
Provision for credit losses		(11)	(14)
Noninterest income		32	31
Noninterest expenses		84	92
Provision (benefit) for income taxes		19	15
Net income (loss)		62	49
Net credit-related charge-offs (recoveries)		13	5
Assets, average		10,920	10,373
Loans, average		10,270	9,830
Deposits, average		$ 8,698	$ 9,188
Return on average assets	[1]	2.30%	1.91%
Efficiency ratio	[2]	54.60%	64.71%
Other Markets
Net interest income (expense)		$ 91	$ 78
Provision for credit losses		(8)	(8)
Noninterest income		87	88
Noninterest expenses		91	91
Provision (benefit) for income taxes		19	15
Net income (loss)		76	68
Net credit-related charge-offs (recoveries)		(3)	11
Assets, average		8,852	8,361
Loans, average		8,082	7,640
Deposits, average		$ 7,898	$ 7,670
Return on average assets	[1]	3.48%	3.32%
Efficiency ratio	[2]	50.99%	54.98%
Finance & Other
Net interest income (expense)		$ 1	$ (3)
Provision for credit losses		2	2
Noninterest income		7	13
Noninterest expenses		18	13
Provision (benefit) for income taxes	[3]	(16)	(25)
Net income (loss)		4	20
Net credit-related charge-offs (recoveries)		0	0
Assets, average		17,876	19,615
Loans, average		0	0
Deposits, average		$ 1,262	$ 917

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

[3] Included discrete tax benefits of $11 million and $22 million for the three months ended March 31, 2019 and 2018, respectively.