Loans and Allowance for Loan Losses (Details 10) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Summary of company's TDRs
Total troubled debt restructured loans	$ 512	$ 512	$ 473
Pre- and post-modification outstanding recorded investment amounts of TDRs
Pre-Modification Outstanding Recorded Investment	86	149
Post-Modification Outstanding Recorded Investment	81	143
Recorded investment amounts of TDRs
Recorded investments, Total	9	36
Commercial and Industrial [Member]
Summary of company's TDRs
Total troubled debt restructured loans	171	171	151
Pre- and post-modification outstanding recorded investment amounts of TDRs
Pre-Modification Outstanding Recorded Investment	52	74
Post-Modification Outstanding Recorded Investment	48	70
Recorded investment amounts of TDRs
Recorded investments, Total	1	2
Commercial Mortgage [Member]
Summary of company's TDRs
Total troubled debt restructured loans	110	110	104
Pre- and post-modification outstanding recorded investment amounts of TDRs
Pre-Modification Outstanding Recorded Investment	9	21
Post-Modification Outstanding Recorded Investment	8	19
Recorded investment amounts of TDRs
Recorded investments, Total		1
Construction [Member]
Summary of company's TDRs
Total troubled debt restructured loans	40	40	66
Recorded investment amounts of TDRs
Recorded investments, Total		15
Commercial [Member]
Summary of company's TDRs
Total troubled debt restructured loans	321	321	321
Pre- and post-modification outstanding recorded investment amounts of TDRs
Pre-Modification Outstanding Recorded Investment	61	95
Post-Modification Outstanding Recorded Investment	56	89
Recorded investment amounts of TDRs
Recorded investments, Total	1	18
Residential Mortgage [Member]
Summary of company's TDRs
Total troubled debt restructured loans	184	184	142
Pre- and post-modification outstanding recorded investment amounts of TDRs
Pre-Modification Outstanding Recorded Investment	25	53
Post-Modification Outstanding Recorded Investment	25	53
Recorded investment amounts of TDRs
Recorded investments, Total	8	12
Home Equity and Other Consumer Loans [Member]
Summary of company's TDRs
Total troubled debt restructured loans	3	3	2
Consumer [Member]
Summary of company's TDRs
Total troubled debt restructured loans	187	187	144
Pre- and post-modification outstanding recorded investment amounts of TDRs
Pre-Modification Outstanding Recorded Investment	25	53
Post-Modification Outstanding Recorded Investment	25	53
Recorded investment amounts of TDRs
Recorded investments, Total	8	12
FDIC covered loans [Member]
Summary of company's TDRs
Total troubled debt restructured loans	4	4	8
Pre- and post-modification outstanding recorded investment amounts of TDRs
Pre-Modification Outstanding Recorded Investment		1
Post-Modification Outstanding Recorded Investment		1
Recorded investment amounts of TDRs
Recorded investments, Total		$ 6