Business Segment Information (Market Segment Financial Results) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Net interest income (expense)		$ 549	$ 470
Provision for credit losses		12	16
Noninterest income		244	271
Noninterest expenses		446	457
Provision (benefit) for income taxes		(54)	(66)
Net income (loss)		281	202
Net credit-related charge-offs (recoveries)		28	33
Assets, average		70,326	71,819
Loans, average		48,421	47,900
Deposits, average		$ 56,090	$ 57,779
Return on average assets	[1],[2]	1.62%	1.14%
Efficiency ratio	[3],[4]	56.33%	61.71%
Tax benefits from employee stock transactions		$ 19	$ 24
Michigan
Net interest income (expense)		169	170
Provision for credit losses		33	(2)
Noninterest income		73	83
Noninterest expenses		144	150
Provision (benefit) for income taxes		(16)	(37)
Net income (loss)		49	68
Net credit-related charge-offs (recoveries)		(1)	(3)
Assets, average		13,395	13,254
Loans, average		12,604	12,586
Deposits, average		$ 21,227	$ 22,150
Return on average assets	[2]	0.88%	1.20%
Efficiency ratio	[4]	59.61%	59.50%
California
Net interest income (expense)		$ 180	$ 171
Provision for credit losses		(2)	21
Noninterest income		39	41
Noninterest expenses		106	96
Provision (benefit) for income taxes		(30)	(36)
Net income (loss)		85	59
Net credit-related charge-offs (recoveries)		13	10
Assets, average		18,581	17,958
Loans, average		18,347	17,680
Deposits, average		$ 17,091	$ 17,243
Return on average assets	[2]	1.86%	1.32%
Efficiency ratio	[4]	48.39%	45.25%
Texas
Net interest income (expense)		$ 109	$ 113
Provision for credit losses		(13)	(9)
Noninterest income		31	32
Noninterest expenses		92	94
Provision (benefit) for income taxes		(14)	(22)
Net income (loss)		47	38
Net credit-related charge-offs (recoveries)		5	22
Assets, average		10,373	10,555
Loans, average		9,830	10,111
Deposits, average		$ 9,188	$ 10,113
Return on average assets	[2]	1.85%	1.35%
Efficiency ratio	[4]	65.63%	64.80%
Other Markets
Net interest income (expense)		$ 78	$ 79
Provision for credit losses		(8)	11
Noninterest income		88	100
Noninterest expenses		91	106
Provision (benefit) for income taxes		(15)	(16)
Net income (loss)		68	46
Net credit-related charge-offs (recoveries)		11	4
Assets, average		8,362	8,255
Loans, average		7,640	7,523
Deposits, average		$ 7,668	$ 7,915
Return on average assets	[2]	3.32%	2.13%
Efficiency ratio	[4]	54.97%	59.31%
Finance & Other
Net interest income (expense)		$ 13	$ (63)
Provision for credit losses		2	(5)
Noninterest income		13	15
Noninterest expenses		13	11
Provision (benefit) for income taxes	[5]	21	45
Net income (loss)		32	(9)
Net credit-related charge-offs (recoveries)		0	0
Assets, average		19,615	21,797
Loans, average		0	0
Deposits, average		$ 916	$ 358

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

[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 securities gains (losses).

[4] Noninterest expenses as a percentage of the sum of net interest income and noninterest income excluding net securities gains (losses).

[5] Included tax benefits from employee stock transactions of $19 million and $24 million for the three months ended March 31, 2018 and 2017, respectively.