Loans and ACL - Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for credit losses	$ 150	$ 148
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	522	530
Charge-Offs	(23)	(33)
Recoveries	8	7
Provision for credit losses	15	20
Ending Balance	522	524
Commercial | CRE
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	160	145
Charge-Offs	(6)	(1)
Recoveries	2	6
Provision for credit losses	19	(9)
Ending Balance	175	141
Commercial | Lease financing
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	9	7
Charge-Offs	(1)	(1)
Recoveries	0	0
Provision for credit losses	2	4
Ending Balance	10	10
Retail | Residential mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	209	227
Charge-Offs	(4)	(12)
Recoveries	0	0
Provision for credit losses	11	8
Ending Balance	216	223
Retail | Direct
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	106	103
Charge-Offs	(19)	(14)
Recoveries	6	6
Provision for credit losses	6	7
Ending Balance	99	102
Retail | Indirect
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	348	327
Charge-Offs	(107)	(107)
Recoveries	15	17
Provision for credit losses	91	101
Ending Balance	347	338
Revolving credit
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	108	106
Charge-Offs	(21)	(21)
Recoveries	5	5
Provision for credit losses	12	13
Ending Balance	104	103
PCI
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	28	44
Charge-Offs	0	0
Recoveries	0	0
Provision for credit losses	(3)	2
Ending Balance	25	46
ALLL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,490	1,489
Charge-Offs	(181)	(189)
Recoveries	36	41
Provision for credit losses	153	146
Ending Balance	1,498	1,487
RUFC
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	119	110
Charge-Offs	0	0
Recoveries	0	0
Provision for credit losses	(3)	2
Ending Balance	116	112
ACL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,609	1,599
Charge-Offs	(181)	(189)
Recoveries	36	41
Provision for credit losses	150	148
Ending Balance	$ 1,614	$ 1,599