Goodwill and Other Intangible Assets (Changes in Carrying Amounts of Goodwill Attributable to Each Operating Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill, beginning balance	$ 6,869	$ 6,814	$ 6,804
Acquisitions	1,726	41	0
Contingent consideration		14	6
Allocated to sale of American Coastal	(49)
Other adjustments	2	0	4
Goodwill, ending balance	8,548	6,869	6,814
Community Banking [Member]
Goodwill, beginning balance	4,634	4,924	4,900
Acquisitions	1,548	29	0
Other adjustments	5	(319)	24
Goodwill, ending balance	6,187	4,634	4,924
Residential Mortgage Banking [Member]
Goodwill, beginning balance	326	7	7
Acquisitions	0	0	0
Other adjustments	0	319	0
Goodwill, ending balance	326	326	7
Dealer Financial Services [Member]
Goodwill, beginning balance	111	111	111
Acquisitions	0	0	0
Other adjustments	0	0	0
Goodwill, ending balance	111	111	111
Specialized Lending [Member]
Goodwill, beginning balance	88	88	99
Acquisitions	155	0	0
Other adjustments	0	0	(11)
Goodwill, ending balance	243	88	88
Insurance Services [Member]
Goodwill, beginning balance	1,518	1,492	1,495
Acquisitions	16	12	0
Contingent consideration	0	14	6
Allocated to sale of American Coastal	(49)
Other adjustments	(3)	0	(9)
Goodwill, ending balance	1,482	1,518	1,492
Financial Services [Member]
Goodwill, beginning balance	192	192	192
Acquisitions	7	0	0
Other adjustments	0	0	0
Goodwill, ending balance	$ 199	$ 192	$ 192