Acquisitions and Divestitures (Purchase Price Allocations) (Details) - USD ($) $ in Millions		3 Months Ended
	Aug. 01, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014
Susquehanna [Member]
Cash, due from banks and federal funds sold	$ 304
Securities acquired, fair value	2,592
Loans acquired, fair value	12,910
Goodwill	1,376
CDI acquired, fair value	167
Other assets acquired, fair value	908
Total assets acquired acquired, fair value	18,257
Deposits assumed, fair value	14,131
Debt assumed, fair value	1,222
Other liabilities assumed, fair value	299
Total liabilities assumed, fair value	15,652
Consideration paid (received)	2,605
Cash paid (received)	739
Fair value of common stock issued, including replacement equity awards	1,866
UPB of loans acquired	13,698
Susquehanna [Member] | Noninterest-bearing deposits
Deposits assumed, fair value	2,068
Susquehanna [Member] | Interest-bearing deposits
Deposits assumed, fair value	12,063
Susquehanna [Member] | Commercial and Industrial [Member]
Loans acquired, fair value	3,876
UPB of loans acquired	4,039
Susquehanna [Member] | CRE-Income Producing Properties [Member]
Loans acquired, fair value	2,062
UPB of loans acquired	2,137
Susquehanna [Member] | CRE-Construction And Development [Member]
Loans acquired, fair value	804
UPB of loans acquired	842
Susquehanna [Member] | Commercial Dealer Floor Plan [Member]
Loans acquired, fair value	31
UPB of loans acquired	31
Susquehanna [Member] | Commercial Other Lending Subsidiaries [Member]
Loans acquired, fair value	807
UPB of loans acquired	852
Susquehanna [Member] | Direct Retail Lending [Member]
Loans acquired, fair value	1,836
UPB of loans acquired	1,980
Susquehanna [Member] | Retail Residential Mortgage-Nonguaranteed [Member]
Loans acquired, fair value	1,511
UPB of loans acquired	1,545
Susquehanna [Member] | Retail Sales Finance [Member]
Loans acquired, fair value	1,580
UPB of loans acquired	1,654
Susquehanna [Member] | PCI [Member]
Loans acquired, fair value	403
UPB of loans acquired	$ 618
The Bank of Kentucky [Member]
Cash, due from banks and federal funds sold		$ 135
Securities acquired, fair value		348
Loans acquired, fair value		1,198
Goodwill		234
CDI acquired, fair value		17
Other assets acquired, fair value		94
Total assets acquired acquired, fair value		2,026
Deposits assumed, fair value		1,555
Debt assumed, fair value		73
Other liabilities assumed, fair value		3
Total liabilities assumed, fair value		1,631
Consideration paid (received)		395
Cash paid (received)		73
Fair value of common stock issued, including replacement equity awards		$ 322
Citi 41 Branches in Texas [Member]
Cash, due from banks and federal funds sold			$ 14
Securities acquired, fair value			0
Loans acquired, fair value			61
Goodwill			90
CDI acquired, fair value			26
Other assets acquired, fair value			47
Total assets acquired acquired, fair value			238
Deposits assumed, fair value			1,907
Debt assumed, fair value			0
Other liabilities assumed, fair value			0
Total liabilities assumed, fair value			1,907
Consideration paid (received)			(1,669)
Cash paid (received)			(1,669)
Fair value of common stock issued, including replacement equity awards			$ 0
Citi 21 Branches in Texas [Member]
Cash, due from banks and federal funds sold				$ 6
Securities acquired, fair value				0
Loans acquired, fair value				112
Goodwill				30
CDI acquired, fair value				20
Other assets acquired, fair value				15
Total assets acquired acquired, fair value				183
Deposits assumed, fair value				1,228
Debt assumed, fair value				0
Other liabilities assumed, fair value				0
Total liabilities assumed, fair value				1,228
Consideration paid (received)				(1,045)
Cash paid (received)				(1,045)
Fair value of common stock issued, including replacement equity awards				$ 0