Investments (Narrative) (USD $)	3 Months Ended					3 Months Ended	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Mar. 31, 2012 Borrowed Securities [Member]	Dec. 31, 2011 Borrowed Securities [Member]	Mar. 31, 2012 Collateral Fixed Maturity Securities [Member]	Dec. 31, 2011 Collateral Fixed Maturity Securities [Member]	Mar. 31, 2011 Collateral Fixed Maturity Securities [Member]	Mar. 31, 2012 Canadian Province Of Ontario Securities [Member]	Dec. 31, 2011 Canadian Province Of Ontario Securities [Member]	Mar. 31, 2012 Canadian Province Of Quebec Securities [Member]	Dec. 31, 2011 Canadian Province Of Quebec Securities [Member]	Mar. 31, 2012 Investment Grade Securities [Member]	Dec. 31, 2011 Investment Grade Securities [Member]
Investment Narrative [Line Items]
Proceeds From Sale Of Available For Sale Securities Sold At Loss	$ 248,100,000	$ 196,600,000				$ 30,100,000	$ 1,000,000
Available For Sale Securities Amortized Cost	7,518,983,000		6,931,958,000	150,000,000	150,000,000		29,000,000	37,400,000
Available For Sale Securities Fair Value Disclosure	8,111,454,000		7,461,106,000	150,000,000	150,000,000	41,300,000	32,600,000		1,179,000,000	1,171,200,000	1,083,200,000	1,107,700,000
Percentage Of Total Gross Unrealized Losses													58.90%	65.30%
Mortgage Loan Percent Of Cash And Invested Assets	3.90%	3.80%
Impaired Financing Receivable Interest Income Accrual Method	477,000	285,000
Loans And Leases Receivable Impaired Nonperforming Nonaccrual Of Interest	17,200,000		20,300,000
Available For Sale Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions	851		940
Gross Unrealized Losses On Equity Securities Continuous Unrealized Loss Position Greater Than 20 Percent Greater Than 12 Months Aggregate Losses	500,000		500,000
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses 1	$ 68,800,000		$ 68,600,000
Other Invested Assets Percent Of Cash And Invested Assets	3.30%		3.90%