Accumulated Other Comprehensive Income (Loss) - Changes in Unrealized Capital Gains (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011
Equity [Abstract]
Net unrealized capital gains/losses arising during the period	$ 346.5	[1]	$ 281.9	[1]
Less: reclassification adjustment for gains (losses) and other items included in Net income (loss)	38.7	[2]	65.8	[2]
Change in deferred tax valuation allowance	0		48.0
Net change in unrealized capital gains/losses on securites	307.8		264.1
Pretax net unrealized capital gains/losses	524.6		422.0
Pretax reclassification adjustments for gains and other items included in Net income (loss)	$ 58.6		$ 98.5

[1] Pretax net unrealized capital gains/losses arising during the period were $524.6 and $422.0 for the nine months ended September 30, 2012 and 2011, respectively.

[2] Pretax reclassification adjustments for gains (losses) and other items included in Net income (loss) were $58.6 and $98.5 for the nine months ended September 30, 2012 and 2011, respectively.