Loans and ACL (Analysis of the Allowance for Credit Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Provision (benefit)	$ 428	$ 251	$ 592
Commercial and Industrial [Member]
ACL, beginning balance	421	454	470
Charge-offs	(81)	(131)	(248)
Recoveries	37	42	47
Provision (benefit)	89	56	166
Other			19
ACL, ending balance	466	421	454
CRE-Income Producing Properties [Member]
ACL, beginning balance	162	149	170
Charge-offs	(20)	(31)	(74)
Recoveries	7	14	20
Provision (benefit)	(14)	30	23
Other			10
ACL, ending balance	135	162	149
CRE-Construction And Development [Member]
ACL, beginning balance	48	76	134
Charge-offs	(4)	(11)	(58)
Recoveries	11	19	31
Provision (benefit)	(18)	(36)	(39)
Other			8
ACL, ending balance	37	48	76
Commercial Dealer Floor Plan [Member]
ACL, beginning balance	10	8	2
Charge-offs	0	0	0
Recoveries	0	0	0
Provision (benefit)	(2)	2	6
Other			0
ACL, ending balance	8	10	8
Commercial Other Lending Subsidiaries [Member]
ACL, beginning balance	21	15	13
Charge-offs	(9)	(10)	(3)
Recoveries	3	3	2
Provision (benefit)	7	11	3
Other			0
ACL, ending balance	22	21	15
Direct Retail Lending [Member]
ACL, beginning balance	110	209	300
Charge-offs	(54)	(69)	(148)
Recoveries	29	29	38
Provision (benefit)	20	26	15
Other		(85)	4
ACL, ending balance	105	110	209
Retail Revolving Credit [Member]
ACL, beginning balance	110	115	102
Charge-offs	(70)	(71)	(85)
Recoveries	20	19	17
Provision (benefit)	44	47	81
Other			0
ACL, ending balance	104	110	115
Retail Residential Mortgage-Nonguaranteed [Member]
ACL, beginning balance	217	269	296
Charge-offs	(40)	(82)	(79)
Recoveries	3	7	3
Provision (benefit)	14	(62)	5
Other		85	44
ACL, ending balance	194	217	269
Retail Residential Mortgage-Government Guaranteed [Member]
ACL, beginning balance	36	62	32
Charge-offs	(6)	(2)	(2)
Recoveries	0	0	0
Provision (benefit)	(7)	(24)	32
Other			0
ACL, ending balance	23	36	62
Retail Sales Finance [Member]
ACL, beginning balance	40	37	27
Charge-offs	(26)	(23)	(23)
Recoveries	9	9	9
Provision (benefit)	17	17	24
Other			0
ACL, ending balance	40	40	37
Retail Other Lending Subsidiaries [Member]
ACL, beginning balance	235	224	264
Charge-offs	(277)	(259)	(252)
Recoveries	33	30	32
Provision (benefit)	274	242	245
Other			(65)
ACL, ending balance	265	235	224
PCI [Member]
ACL, beginning balance	64	114	128
Charge-offs	(1)	(21)	(19)
Recoveries	0	0	0
Provision (benefit)	(2)	(29)	5
Other			0
ACL, ending balance	61	64	114
Unallocated [Member]
ACL, beginning balance			80
Charge-offs			0
Recoveries			0
Provision (benefit)			(33)
Other			(47)
ALLL [Member]
ACL, beginning balance	1,474	1,732	2,018
Charge-offs	(588)	(710)	(991)
Recoveries	152	172	199
Provision (benefit)	422	280	533
Other			(27)
ACL, ending balance	1,460	1,474	1,732
RUFC [Member]
ACL, beginning balance	60	89	30
Charge-offs	0	0	0
Recoveries	0	0	0
Provision (benefit)	6	(29)	59
Other	24		0
ACL, ending balance	90	60	89
ACL [Member]
ACL, beginning balance	1,534	1,821	2,048
Charge-offs	(588)	(710)	(991)
Recoveries	152	172	199
Provision (benefit)	428	251	592
Other	24		(27)
ACL, ending balance	$ 1,550	$ 1,534	$ 1,821