Share Capital (Detail) (USD $)	3 Months Ended			6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2011	Mar. 31, 2011	Mar. 31, 2010	Jun. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Treasury stock repurchase limit							$ 1,000,000,000
Treasury Stock, Shares, Retired (in Shares)	15,100,000			11,600,000			6,900,000
Treasury Stock, Retired, Cost Method, Amount	307,700,000			257,900,000			144,000,000
Treasury Stock, Value, Acquired, Cost Method	290,400,000
Rate of interest of Equity security Units					10.75%
Equity Unit Note Coupon Rate					8.25%
Senior Notes	575,000,000				575,000,000
Equity Security Unit Settlement Shares (in Shares)					1.3242
Face Value Of Equity Security Unit Issued (in Dollars per share)					$ 25
Proceeds from Issuance of Senior Long-term Debt					600,000,000
Debt Instrument, Interest Rate, Effective Percentage	6.50%				6.50%
Stock Repurchased and Retired During Period, Shares (in Shares)					2,811,000
Preferred Stock, Liquidation Preference Per Share (in Dollars per share)	$ 25				$ 25
Payments for Repurchase of Redeemable Preferred Stock			94,200,000		71,801,000	94,157,000
Noncontrolling Interest, Period Increase (Decrease)		130,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures (in Shares)					1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in Dollars per share)					$ 9.82
Share Based Compensation Arrangement By Share Based Payment Award Restricted Stock Units Grants In Period Weighted Average Grant Date Shares (in Shares)					1,200,000
Share Based Compensation Arrangement By Share Based Payment Award Restricted Stock Units Grants In Period Weighted Average Grant Date Fair Value					26,600,000
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures (in Shares)					46,062
Share Based Compensation Arrangement By Share Based Payment Award Restricted Stock Awards Grants In Period Weighted Average Grant Date Fair Value					1,100,000
Minimum Percentage Target Pay out Under Performance Unit Grants In Period					0.00%
Maximum Percentage Target Pay out Under Performance Unit Grants In Period					200.00%
Relating To Settlement of Purchase of Contracts [Member] | Common Class A [Member]
Stock Issued During Period, Shares, New Issues (in Shares)					30,456,600
Performance Incentive Program [Member]
Share Based Compensation Arrangement By Share Based Payment Award Restricted Stock Units Grants In Period Weighted Average Grant Date Fair Value					28,500,000
Share Based Compensation Arrangement By Share Based Payment Award Performance Unit Grants In Period					1,300,000
Maximum Limit Share Pay out Under Performance Unit Grants In Period					2,600,000
Series D Preferred Stock [Member]
Shares Issuable, Value, Consideration of Cash and Liquid Investments	350,000,000
Preferred Stock, Dividend Payment Rate, Variable					three-month LIBOR plus 3.120%
Series C Preferred Stock [Member]
Treasury Stock, Retired, Cost Method, Amount					900,000
Stock Repurchased and Retired During Period, Shares (in Shares)		30,000	4,400,000
Stock Repurchased and Retired During Period, Value					71,000,000
Liquidation value of preferred shares repurchased		750,000	110,800,000
Payments for Repurchase of Redeemable Preferred Stock		650,000
Book value gain on repurchase of preferred stock			16,600,000
Series E Preferred Stock [Member]
Stock Repurchased and Retired During Period, Shares (in Shares)		500
Liquidation value of preferred shares repurchased		500,000
Payments for Repurchase of Preferred Stock and Preference Stock		$ 470,000