Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Corporation's Portfolio of Commercial Real Estate Loans) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Schedule of Commercial Real Estate Loans [Line Items]
Real estate construction loans	$ 1,533		$ 2,253
Commercial mortgage loans	10,264		9,767
Total commercial real estate loans	41,953		39,335
Commercial Real Estate [Member]
Schedule of Commercial Real Estate Loans [Line Items]
Total commercial real estate loans	11,797		12,020
Total unused commitments on commercial real estate loans	690		707
Real Estate Construction Loans [Member] | Commercial Real Estate Business Line [Member]
Schedule of Commercial Real Estate Loans [Line Items]
Real estate construction loans	1,103	[1]	1,826	[1]
Real Estate Construction Loans [Member] | Other Business Lines [Member]
Schedule of Commercial Real Estate Loans [Line Items]
Real estate construction loans	430	[2]	427	[2]
Commercial Mortgage Loans [Member] | Commercial Real Estate Business Line [Member]
Schedule of Commercial Real Estate Loans [Line Items]
Commercial mortgage loans	2,507	[1]	1,937	[1]
Commercial Mortgage Loans [Member] | Other Business Lines [Member]
Schedule of Commercial Real Estate Loans [Line Items]
Commercial mortgage loans	$ 7,757	[2]	$ 7,830	[2]

[1] (a)Primarily loans to real estate investors and developers.

[2] (b)Primarily loans secured by owner-occupied real estate.