Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Commercial Real Estate Exposure) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 45,470		$ 46,057
Real estate construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,762		1,240
Commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,787		9,472
Total commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,549		10,712
Total unused commitments	1,780		1,523
Commercial Real Estate business line | Real estate construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,447	[1]	1,049	[1]
Commercial Real Estate business line | Commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,678	[1]	1,873	[1]
Other business lines | Real estate construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	315	[2]	191	[2]
Other business lines | Commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 7,109	[2]	$ 7,599	[2]

[1] Primarily loans to real estate developers.

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