Business Segment Information (Market Segment Financial Results) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Net interest income (expense)		$ 545	$ 546	$ 500	$ 470	$ 455	$ 450	$ 445	$ 447	$ 2,061		$ 1,797	$ 1,689
Provision for credit losses										74		248	147
Noninterest income										1,107		1,051	1,035
Noninterest expenses		483	463	457	457	461	493	518	458	1,860		1,930	1,827
Provision (benefit) for income taxes		(218)	(108)	(99)	(66)	(62)	(64)	(42)	(25)	(491)		(193)	(229)
Net income (loss)		$ 112	$ 226	$ 203	$ 202	$ 164	$ 149	$ 104	$ 60	743		477	521
Net loan charge-offs (recoveries)										92		157	101
Assets, average										71,452		71,743	70,247
Loans, average										48,558		48,996	48,628
Deposits, average										$ 57,258		$ 57,741	$ 58,326
Return on average assets	[1],[2]									1.04%		0.67%	0.74%
Efficiency ratio	[3],[4]									58.57%		67.53%	66.93%
Remeasurement of deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act										$ (107)		$ 0	$ 0
Income tax benefit related to employee stock transactions										(35)		0	0
Michigan
Net interest income (expense)										685		666	708
Provision for credit losses										8		9	(27)
Noninterest income										324		320	329
Noninterest expenses										590		620	594
Provision (benefit) for income taxes										(147)		(114)	(151)
Net income (loss)										264		243	319
Net loan charge-offs (recoveries)										(1)		9	8
Assets, average										13,395		13,105	13,598
Loans, average										12,677		12,457	13,016
Deposits, average										$ 21,823		$ 21,777	$ 21,848
Return on average assets	[2]									1.17%		1.08%	1.40%
Efficiency ratio	[4]									58.30%		62.33%	56.93%
California
Net interest income (expense)										$ 719		$ 716	$ 735
Provision for credit losses										100		21	17
Noninterest income										171		162	150
Noninterest expenses										404		434	405
Provision (benefit) for income taxes										(148)		(152)	(166)
Net income (loss)										238		271	297
Net loan charge-offs (recoveries)										33		26	18
Assets, average										18,269		18,012	17,044
Loans, average										18,008		17,731	16,778
Deposits, average										$ 17,533		$ 17,438	$ 17,788
Return on average assets	[2]									1.29%		1.46%	1.57%
Efficiency ratio	[4]									45.26%		49.55%	45.88%
Texas
Net interest income (expense)										$ 465		$ 470	$ 518
Provision for credit losses										(72)		225	131
Noninterest income										131		129	131
Noninterest expenses										375		408	387
Provision (benefit) for income taxes										(109)		12	(54)
Net income (loss)										184		(22)	77
Net loan charge-offs (recoveries)										46		118	46
Assets, average										10,443		11,101	11,778
Loans, average										9,969		10,637	11,168
Deposits, average										$ 9,625		$ 10,168	$ 10,882
Return on average assets	[2]									1.69%		(0.18%)	0.62%
Efficiency ratio	[4]									62.80%		67.94%	59.63%
Other Markets
Net interest income (expense)										$ 331		$ 350	$ 336
Provision for credit losses										36		(7)	25
Noninterest income										423		393	381
Noninterest expenses										449		445	431
Provision (benefit) for income taxes										(75)		(81)	(64)
Net income (loss)										194		224	197
Net loan charge-offs (recoveries)										14		4	29
Assets, average										8,573		9,062	8,708
Loans, average										7,904		8,171	7,673
Deposits, average										$ 7,874		$ 8,005	$ 7,403
Return on average assets	[2]									2.25%		2.47%	2.26%
Efficiency ratio	[4]									59.57%		59.86%	59.92%
Finance & Other
Net interest income (expense)										$ (139)		$ (405)	$ (608)
Provision for credit losses										2		0	1
Noninterest income										58		47	44
Noninterest expenses										42		23	10
Provision (benefit) for income taxes										(12)	[5]	142	206
Net income (loss)										(137)		(239)	(369)
Net loan charge-offs (recoveries)										0		0	0
Assets, average										20,772		20,463	19,119
Loans, average										0		0	(7)
Deposits, average										403		353	405
Accounting Standards Update 2018-01 | Finance & Other
Remeasurement of deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act										(107)
Accounting Standards Update 2016-09
Income tax benefit related to employee stock transactions										35		$ 4	$ 3
Accounting Standards Update 2016-09 | Finance & Other
Income tax benefit related to employee stock transactions										$ 35

[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 (fully taxable equivalent basis) and noninterest income excluding net securities gains.

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

[5] Included a $107 million charge to adjust deferred taxes as a result of the enactment of the Tax Cuts and Jobs Act and a $35 million tax benefit from employee stock transactions.