Income Taxes - Federal Income Tax Treatment of Share Distributions (Parenthetical) (Detail)	0 Months Ended	12 Months Ended	0 Months Ended
	Apr. 11, 2013 Series J Preferred Stock [Member]	Dec. 31, 2013 Series J Preferred Stock [Member]	Apr. 11, 2013 Depositary Shares [Member] Series J Preferred Stock [Member]	Dec. 21, 2012 Depositary Shares [Member] Series J Preferred Stock [Member]	Jul. 18, 2013 Depositary Shares [Member] Series K Preferred Stock [Member]
Income Tax [Line Items]
Depositary shares of preferred stock redeemed	4,000,000	2,000,000	4,000,000	2,000,000	2,000,000