Business Changes, Risks, Uncertainties and Accounting Developments (Details) (USD $)	1 Months Ended		12 Months Ended		36 Months Ended	1 Months Ended
	Dec. 31, 2009	Jun. 30, 2009 offering	Dec. 31, 2011	Dec. 31, 2009	Dec. 31, 2011	Jul. 31, 2009 AGMH	Jul. 01, 2009 AGMH
Business Changes, Risks, Uncertainties and Accounting Developments
Period of volatility and disruption in global financial markets (in years)			3 years		3 years
Number of offerings		2
Net proceeds from issuance of common stock and equity units		$ 616,500,000		$ 1,190,100,000
Proceeds from equity unit offering		170,800,000		167,972,000
Proceeds from equity unit offering recognized as long-term debt		168,000,000
Proceeds from equity unit offering recognized as additional paid-in capital		2,800,000
Offering costs		43,500,000
Offering costs recorded within additional paid-in capital		41,800,000
Common share issued	27,500,000	44,300,000			82,400,000
Net proceeds from issuance of common shares	573,800,000	448,900,000		1,022,096,000	1,271,700,000
Proceeds from issuance of debt					170,800,000
Most significant events with material impact, period (in years)			3 years
Significant GAAP rule making activity, period (in years)			3 years
Acquisition
Purchase price paid in cash							546,000,000
Number of common shares issued for acquisition						22,300,000
Acquisition date fair value of common shares issued for acquisition							275,900,000
Total purchase price							$ 821,900,000
Period for which operating and financial constraints continue after closing of acquisition (in years)							3 years
Maximum dividends allowed under purchase agreement, expressed as a percentage of debt service requirements							125.00%