Investments - Loans by Debt Service Coverage Ratio (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Benchmark debt service coverage ratio, less than indicates property's operations income is less than debt payments	100.00%
Commercial mortgage loans secured by land or construction loans	$ 8.0	[1]	$ 0.2	[1]
Total Commercial mortgage loans	9,953.1	[1]	9,316.0	[1]
Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Debt Service Coverage Ratio, minimum	150.00%		150.00%
Commercial mortgage loans	7,114.2	[1]	6,346.5	[1]
1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Debt Service Coverage Ratio, minimum	125.00%		125.00%
Debt Service Coverage Ratio, maximum	150.00%		150.00%
Commercial mortgage loans	1,595.1	[1]	1,520.9	[1]
1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Debt Service Coverage Ratio, minimum	100.00%		100.00%
Debt Service Coverage Ratio, maximum	125.00%		125.00%
Commercial mortgage loans	901.1	[1]	980.6	[1]
Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Debt Service Coverage Ratio, maximum	100.00%		100.00%
Commercial mortgage loans	$ 334.7	[1]	$ 467.8	[1]

[1] Balances do not include collective valuation allowance for losses.