Subsequent Events - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Jun. 30, 2012
Capital Trust V
Subsequent Event [Line Items]
Trust Preferred Securities Redemption Amount	$ 575.0
Redemption date	Aug. 15, 2012
Distribution rate	7.25%
Redemption price, per share	$ 25
Unpaid or accrued distribution factor through the actual redemption date	$ 0.453125
Maturity date	Aug. 15, 2067
Unamortized Debt Issuance Costs	17
Capital Trust VI
Subsequent Event [Line Items]
Trust Preferred Securities Redemption Amount	862.5
Redemption date	Aug. 08, 2012
Distribution rate	7.25%
Redemption price, per share	$ 25
Unpaid or accrued distribution factor through the actual redemption date	$ 0.422917
Maturity date	Nov. 15, 2067
Unamortized Debt Issuance Costs	$ 9