Operating Segments (Reportable Segments) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		$ 6,321	$ 5,592	$ 5,374
Allocated provision for credit losses		572	428	251
Noninterest income		4,472	4,019	3,856
Noninterest expense		6,571	6,161	5,761
Amortization of intangibles		150	105	91
Income (loss) before income taxes		3,500	2,917	3,127
Provision (benefit) for income taxes		1,058	794	921
Net income		2,442	2,123	2,206
Identifiable assets (period end)		219,276	209,947	186,834
Community Banking
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		2,208	1,798	1,726
Residential Mortgage Banking
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		1,341	1,357	1,482
Dealer Financial Services
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		930	881	835
Specialized Lending
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		752	648	575
Insurance Holdings
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		3	2	2
Financial Services
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		260	219	187
Other, Treasury and Corporate
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)	[1]	827	687	567
Operating Segments | Community Banking
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		3,797	3,069	2,914
Allocated provision for credit losses		36	67	123
Noninterest income		1,227	1,166	1,184
Noninterest expense		1,742	1,516	1,428
Amortization of intangibles		74	39	29
Allocated corporate expenses		1,337	1,225	1,204
Income (loss) before income taxes		1,988	1,523	1,434
Provision (benefit) for income taxes		724	563	524
Net income		1,264	960	910
Identifiable assets (period end)		73,640	68,250	55,495
Operating Segments | Residential Mortgage Banking
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		443	452	498
Allocated provision for credit losses		45	9	(107)
Noninterest income		344	355	310
Noninterest expense		211	321	498
Amortization of intangibles		0	0	0
Allocated corporate expenses		107	93	91
Income (loss) before income taxes		425	386	328
Provision (benefit) for income taxes		161	146	124
Net income		264	240	204
Identifiable assets (period end)		33,473	33,407	34,463
Operating Segments | Dealer Financial Services
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		769	728	675
Allocated provision for credit losses		296	253	237
Noninterest income		2	0	2
Noninterest expense		149	151	114
Amortization of intangibles		0	0	0
Allocated corporate expenses		45	38	31
Income (loss) before income taxes		281	286	295
Provision (benefit) for income taxes		107	109	112
Net income		174	177	183
Identifiable assets (period end)		16,556	15,130	12,821
Operating Segments | Specialized Lending
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		469	413	369
Allocated provision for credit losses		70	43	36
Noninterest income		297	260	222
Noninterest expense		300	254	210
Amortization of intangibles		5	4	5
Allocated corporate expenses		81	63	62
Income (loss) before income taxes		310	309	278
Provision (benefit) for income taxes		74	74	63
Net income		236	235	215
Identifiable assets (period end)		19,976	18,243	15,671
Operating Segments | Insurance Holdings
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		7	8	8
Allocated provision for credit losses		0	0	0
Noninterest income		1,726	1,608	1,663
Noninterest expense		1,312	1,190	1,189
Amortization of intangibles		60	47	53
Allocated corporate expenses		111	99	86
Income (loss) before income taxes		250	280	343
Provision (benefit) for income taxes		96	98	110
Net income		154	182	233
Identifiable assets (period end)		3,463	2,804	2,965
Operating Segments | Financial Services
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		632	533	450
Allocated provision for credit losses		126	66	26
Noninterest income		888	850	780
Noninterest expense		753	683	637
Amortization of intangibles		5	3	2
Allocated corporate expenses		151	136	128
Income (loss) before income taxes		508	517	452
Provision (benefit) for income taxes		190	195	170
Net income		318	322	282
Identifiable assets (period end)		17,451	16,650	12,887
Operating Segments | Other, Treasury and Corporate
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)	[1]	204	389	460
Allocated provision for credit losses	[1]	(1)	(10)	(64)
Noninterest income	[1]	(12)	(220)	(305)
Noninterest expense	[1]	2,104	2,046	1,685
Amortization of intangibles	[1]	6	12	2
Allocated corporate expenses	[1]	(1,832)	(1,654)	(1,602)
Income (loss) before income taxes	[1]	(262)	(384)	(3)
Provision (benefit) for income taxes	[1]	(294)	(391)	(182)
Net income	[1]	32	7	179
Identifiable assets (period end)	[1]	54,717	55,463	52,532
Intersegment Eliminations | Community Banking
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		1,589	1,271	1,188
Intersegment net referral fees (expense)		153	135	120
Intersegment Eliminations | Residential Mortgage Banking
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		(898)	(905)	(984)
Intersegment net referral fees (expense)		1	2	2
Intersegment Eliminations | Dealer Financial Services
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		(161)	(153)	(160)
Intersegment net referral fees (expense)		0	0	0
Intersegment Eliminations | Specialized Lending
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		(283)	(235)	(206)
Intersegment net referral fees (expense)		0	0	0
Intersegment Eliminations | Insurance Holdings
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		4	6	6
Intersegment net referral fees (expense)		0	0	0
Intersegment Eliminations | Financial Services
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)		372	314	263
Intersegment net referral fees (expense)		23	22	15
Intersegment Eliminations | Other, Treasury and Corporate
Segment Reporting, Revenue Reconciling Items [Line Items]
Net interest income (expense)	[1]	(623)	(298)	(107)
Intersegment net referral fees (expense)	[1]	$ (177)	$ (159)	$ (137)

[1] (1) Includes financial data from subsidiaries below the quantitative and qualitative thresholds requiring disclosure.