Non-Controlling Interests, Preferred Shares, Common Shares and Common Shares in Treasury - Common Shares Through Open Market Sales (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Equity Offerings [Line Items]
Number of Shares Sold	36.5	9.5	53.0
Average Price Per Share	$ 13.98	$ 13.71	$ 8.33
Net Proceeds	$ 493.2	$ 129.7	$ 441.3