Loans and ACL - Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision (Benefit)	$ 184	$ 99
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	466	421
Charge-Offs	(56)	(14)
Recoveries	12	8
Provision (Benefit)	77	33
Ending Balance	499	448
CRE-income producing properties
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	135	162
Charge-Offs	(2)	(9)
Recoveries	3	2
Provision (Benefit)	(11)	(2)
Ending Balance	125	153
CRE-construction and development
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	37	48
Charge-Offs	0	(2)
Recoveries	1	4
Provision (Benefit)	(6)	(8)
Ending Balance	32	42
Dealer floor plan
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	8	10
Charge-Offs	0	0
Recoveries	0	0
Provision (Benefit)	2	0
Ending Balance	10	10
Commercial other lending subsidiaries
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	22	21
Charge-Offs	(8)	(3)
Recoveries	2	1
Provision (Benefit)	10	3
Ending Balance	26	22
Direct retail lending
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	105	110
Charge-Offs	(13)	(12)
Recoveries	7	8
Provision (Benefit)	4	5
Ending Balance	103	111
Revolving credit
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	104	110
Charge-Offs	(19)	(18)
Recoveries	5	5
Provision (Benefit)	10	9
Ending Balance	100	106
Residential mortgage-nonguaranteed
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	194	217
Charge-Offs	(7)	(11)
Recoveries	1	0
Provision (Benefit)	9	(6)
Ending Balance	197	200
Residential mortgage-government guaranteed
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	23	36
Charge-Offs	(1)	0
Recoveries	0	0
Provision (Benefit)	2	(6)
Ending Balance	24	30
Sales finance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	40	40
Charge-Offs	(8)	(6)
Recoveries	3	3
Provision (Benefit)	4	11
Ending Balance	39	48
Other lending subsidiaries
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	265	235
Charge-Offs	(84)	(64)
Recoveries	10	8
Provision (Benefit)	79	58
Ending Balance	270	237
PCI
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	61	64
Charge-Offs	0	(1)
Recoveries	0	0
Provision (Benefit)	2	(6)
Ending Balance	63	57
ALLL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,460	1,474
Charge-Offs	(198)	(140)
Recoveries	44	39
Provision (Benefit)	182	91
Ending Balance	1,488	1,464
RUFC
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	90	60
Charge-Offs	0	0
Recoveries	0	0
Provision (Benefit)	2	8
Ending Balance	92	68
ACL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,550	1,534
Charge-Offs	(198)	(140)
Recoveries	44	39
Provision (Benefit)	184	99
Ending Balance	$ 1,580	$ 1,532