Loans and Allowance for Loan Losses (Details 6) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Aging of loans
Loans covered under a loss share agreement with FDIC	$ 199	$ 251
Commercial Loan
Aging of loans
Loans covered under a loss share agreement with FDIC	167	213
Total loans	40,743	38,674
Commercial portfolio
Aging of loans
Total loans	40,380	38,060
Commercial portfolio | Commercial and industrial
Aging of loans
Total loans	25,743	24,235
Commercial portfolio | Construction
Aging of loans
Total loans	1,263	893
Commercial portfolio | Commercial mortgage
Aging of loans
Total loans	13,374	12,932
Purchased credit-impaired loans | Commercial Loan
Aging of loans
Total loans	363	614
Pass | Commercial Loan
Aging of loans
Total loans	38,979	36,835
Pass | Commercial portfolio
Aging of loans
Total loans	38,930	36,787
Pass | Commercial portfolio | Commercial and industrial
Aging of loans
Total loans	24,701	23,346
Pass | Commercial portfolio | Construction
Aging of loans
Total loans	1,254	879
Pass | Commercial portfolio | Commercial mortgage
Aging of loans
Total loans	12,975	12,562
Pass | Purchased credit-impaired loans | Commercial Loan
Aging of loans
Total loans	49	48
Special Mention | Commercial Loan
Aging of loans
Total loans	921	936
Special Mention | Commercial portfolio
Aging of loans
Total loans	794	732
Special Mention | Commercial portfolio | Commercial and industrial
Aging of loans
Total loans	603	576
Special Mention | Commercial portfolio | Construction
Aging of loans
Total loans	9	14
Special Mention | Commercial portfolio | Commercial mortgage
Aging of loans
Total loans	182	142
Special Mention | Purchased credit-impaired loans | Commercial Loan
Aging of loans
Total loans	127	204
Classified | Commercial Loan
Aging of loans
Total loans	843	903
Classified | Commercial portfolio
Aging of loans
Total loans	656	541
Classified | Commercial portfolio | Commercial and industrial
Aging of loans
Total loans	439	313
Classified | Commercial portfolio | Commercial mortgage
Aging of loans
Total loans	217	228
Classified | Purchased credit-impaired loans | Commercial Loan
Aging of loans
Total loans	$ 187	$ 362