Income Taxes - Federal Income Tax Treatment of Share Distributions (Parenthetical) (Detail)	Apr. 11, 2013	Dec. 21, 2012	Jul. 18, 2013
Series J Preferred Stock
Income Tax [Line Items]
Depositary shares of preferred stock redeemed	4,000,000	2,000,000
Depositary Shares | Series J Preferred Stock
Income Tax [Line Items]
Depositary shares of preferred stock redeemed	4,000,000	2,000,000
Depositary Shares | Series K Preferred Stock
Income Tax [Line Items]
Depositary shares of preferred stock redeemed			2,000,000