Accumulated Other Comprehensive Income (Loss) - Changes in Unrealized Capital Gains (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Equity [Abstract]
Net unrealized capital gains/losses arising during the year	$ 320.6	[1]	$ 408.8	[1]	$ 335.6	[1]
Less: reclassification adjustment for gains (losses) and other items included in Net income (loss)	43.6	[2]	78.7	[2]	29.2	[2]
Change in deferred tax valuation allowance	0		22.0		68.7
Net change in unrealized capital gains/losses on securites	277.0		352.1		375.1
Pretax net unrealized capital gains/losses	485.4		625.1		495.7
Pretax reclassification adjustments for gains and other items included in Net income (loss)	$ 66.1		$ 120.0		$ 42.8

[1] Pretax net unrealized capital gains/losses arising during the period were $485.4, $625.1 and $495.7 for the years ended December 31, 2012, 2011 and 2010, respectively.

[2] Pretax reclassification adjustments for gains (losses) and other items included in Net income (loss) were $66.1, $120.0 and $42.8 for the years ended December 31, 2012, 2011 and 2010, respectively.