Operating Segments (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		$ 1,647	$ 1,610	$ 4,891	$ 4,756
Allocated provision for credit losses		126	148	409	443
Segment net interest income after provision		1,521	1,462	4,482	4,313
Noninterest income		1,166	1,164	3,557	3,310
Noninterest expense		1,745	1,711	5,589	5,053
Income before income taxes		942	915	2,450	2,570
Provision for income taxes		294	273	702	771
Net income		648	642	1,748	1,799
Identifiable assets (period end)		220,340	222,622	220,340	222,622	$ 219,276
Community Banking
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		647	570	1,852	1,631
Residential Mortgage Banking
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		332	359	996	1,045
Dealer Financial Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		242	229	727	684
Specialized Lending
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		189	177	545	517
Insurance Holdings
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		1	1	2	2
Financial Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		81	65	222	196
Other, Treasury & Corporate (1)
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)	[1]	155	209	547	681
Operating Segments | Community Banking
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		1,056	981	3,088	2,841
Allocated provision for credit losses		23	(3)	111	10
Segment net interest income after provision		1,033	984	2,977	2,831
Noninterest income		373	360	1,104	1,027
Noninterest expense		789	803	2,398	2,356
Income before income taxes		617	541	1,683	1,502
Provision for income taxes		221	197	602	547
Net income		396	344	1,081	955
Identifiable assets (period end)		74,493	73,125	74,493	73,125
Operating Segments | Residential Mortgage Banking
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		123	144	363	399
Allocated provision for credit losses		2	9	17	31
Segment net interest income after provision		121	135	346	368
Noninterest income		86	117	234	272
Noninterest expense		100	40	314	259
Income before income taxes		107	212	266	381
Provision for income taxes		40	80	99	144
Net income		67	132	167	237
Identifiable assets (period end)		33,213	36,652	33,213	36,652
Operating Segments | Dealer Financial Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		196	190	590	566
Allocated provision for credit losses		78	76	254	210
Segment net interest income after provision		118	114	336	356
Noninterest income		0	1	0	2
Noninterest expense		57	50	169	143
Income before income taxes		61	65	167	215
Provision for income taxes		23	25	62	82
Net income		38	40	105	133
Identifiable assets (period end)		15,239	15,090	15,239	15,090
Operating Segments | Specialized Lending
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		108	109	315	316
Allocated provision for credit losses		15	18	43	51
Segment net interest income after provision		93	91	272	265
Noninterest income		71	80	210	212
Noninterest expense		94	92	278	259
Income before income taxes		70	79	204	218
Provision for income taxes		16	19	45	50
Net income		54	60	159	168
Identifiable assets (period end)		18,854	17,823	18,854	17,823
Operating Segments | Insurance Holdings
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		1	0	3	(2)
Allocated provision for credit losses		0	0	0	0
Segment net interest income after provision		1	0	3	(2)
Noninterest income		399	412	1,344	1,298
Noninterest expense		378	375	1,163	1,109
Income before income taxes		22	37	184	187
Provision for income taxes		9	16	70	72
Net income		13	21	114	115
Identifiable assets (period end)		3,360	3,342	3,360	3,342
Operating Segments | Financial Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		161	156	485	452
Allocated provision for credit losses		7	32	(9)	128
Segment net interest income after provision		154	124	494	324
Noninterest income		251	235	711	654
Noninterest expense		237	230	709	677
Income before income taxes		168	129	496	301
Provision for income taxes		62	48	183	113
Net income		106	81	313	188
Identifiable assets (period end)		18,774	17,570	18,774	17,570
Operating Segments | Other, Treasury & Corporate (1)
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)	[1]	2	30	47	184
Allocated provision for credit losses	[1]	1	16	(7)	13
Segment net interest income after provision	[1]	1	14	54	171
Noninterest income	[1]	(14)	(41)	(46)	(155)
Noninterest expense	[1]	90	121	558	250
Income before income taxes	[1]	(103)	(148)	(550)	(234)
Provision for income taxes	[1]	(77)	(112)	(359)	(237)
Net income	[1]	(26)	(36)	(191)	3
Identifiable assets (period end)	[1]	56,407	59,020	56,407	59,020
Intersegment Eliminations | Community Banking
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		409	411	1,236	1,210
Intersegment Eliminations | Residential Mortgage Banking
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		(209)	(215)	(633)	(646)
Intersegment Eliminations | Dealer Financial Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		(46)	(39)	(137)	(118)
Intersegment Eliminations | Specialized Lending
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		(81)	(68)	(230)	(201)
Intersegment Eliminations | Insurance Holdings
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		0	(1)	1	(4)
Intersegment Eliminations | Financial Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)		80	91	263	256
Intersegment Eliminations | Other, Treasury & Corporate (1)
Segment Reporting, Revenue Reconciling Item [Line Items]
Net interest income (expense)	[1]	$ (153)	$ (179)	$ (500)	$ (497)

[1] Includes financial data from business units below the quantitative and qualitative thresholds requiring disclosure.