Preferred Stock - Additional Information (Details) (USD $)	0 Months Ended	12 Months Ended
	Oct. 01, 2007	Dec. 31, 2014
Floating Rate Non-Cumulative Preferred Stock, Series F ($25 stated value) [Member]
Class of Stock [Line Items]
Stated Value Per Share (usd per share)		$ 25
Dividend Rate		3.549%
14,950,000 Depositary Shares each representing a one-fortieth interest in a share of Floating Rate Non-Cumulative Preferred Stock, Series G ($1,000 stated value) [Member]
Class of Stock [Line Items]
Stated Value Per Share (usd per share)		$ 1,000
Preferred Stock, Depositary Shares Outstanding (sharers)		14,950,000
Dividend Rate		4.056%
Ownership interest		2.50%
14,950,000 Depositary Shares each representing a one-fortieth interest in a share of 6.50% Non-Cumulative Preferred Stock, Series H ($1,000 stated value) [Member]
Class of Stock [Line Items]
Stated Value Per Share (usd per share)		$ 1,000
Preferred Stock, Depositary Shares Outstanding (sharers)		14,950,000
Dividend Rate		6.50%
Ownership interest		2.50%
6,000,000 Depositary shares each representing a one-fourth interest in a share of Adjustable Rate Cumulative Preferred Stock, Series D ($100 stated value) [Member]
Class of Stock [Line Items]
Stated Value Per Share (usd per share)		$ 100
Preferred Stock, Depositary Shares Outstanding (sharers)		6,000,000
Dividend Rate		4.50%
Ownership interest		25.00%
$2.8575 Cumulative Preferred Stock ($50 stated value) [Member]
Class of Stock [Line Items]
Stated Value Per Share (usd per share)		$ 50
Dividend Rate		5.715%
Dividend per share (usd per share)	$ 2.8575	$ 2.8575