Goodwill and Other Intangible Assets - Goodwill Activity by Operating Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 9,638	$ 8,548	$ 6,869
Acquired goodwill, net		1,073	1,726
American Coastal sale			(49)
Other adjustments	(20)	17	2
Goodwill, ending balance	9,618	9,638	8,548
Community Banking
Goodwill [Roll Forward]
Goodwill, beginning balance	7,032	6,140	4,634
Acquired goodwill, net		753	1,501
American Coastal sale			0
Other adjustments	(12)	139	5
Goodwill, ending balance	7,020	7,032	6,140
Residential Mortgage Banking
Goodwill [Roll Forward]
Goodwill, beginning balance	416	369	326
Acquired goodwill, net		39	43
American Coastal sale			0
Other adjustments	6	8	0
Goodwill, ending balance	422	416	369
Dealer Financial Services
Goodwill [Roll Forward]
Goodwill, beginning balance	111	111	111
Acquired goodwill, net		0	0
American Coastal sale			0
Other adjustments	0	0	0
Goodwill, ending balance	111	111	111
Specialized Lending
Goodwill [Roll Forward]
Goodwill, beginning balance	113	243	88
Acquired goodwill, net		2	155
American Coastal sale			0
Other adjustments	(9)	(132)	0
Goodwill, ending balance	104	113	243
Insurance Holdings
Goodwill [Roll Forward]
Goodwill, beginning balance	1,752	1,482	1,518
Acquired goodwill, net		270	16
American Coastal sale			(49)
Other adjustments	(5)	0	(3)
Goodwill, ending balance	1,747	1,752	1,482
Financial Services
Goodwill [Roll Forward]
Goodwill, beginning balance	214	203	192
Acquired goodwill, net		9	11
American Coastal sale			0
Other adjustments	0	2	0
Goodwill, ending balance	214	$ 214	$ 203
CB-Retail
Goodwill [Roll Forward]
Goodwill, ending balance	3,724
CB-Commercial
Goodwill [Roll Forward]
Goodwill, ending balance	3,862
FS&CF
Goodwill [Roll Forward]
Goodwill, ending balance	259
IH&PF
Goodwill [Roll Forward]
Goodwill, ending balance	$ 1,773