Accumulated Other Comprehensive Income (Loss) - Changes in Unrealized Capital Gains (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011
Equity [Abstract]
Net unrealized capital gains/losses arising during the period	$ 172.2	[1]	$ 122.6	[1]
Less: reclassification adjustment for gains (losses) and other items included in Net income (loss)	36.9	[2]	50.3	[2]
Change in deferred tax valuation allowance	10.0		5.4
Net change in unrealized capital gains/losses on securites	145.3		77.7
Pretax net unrealized capital gains/losses	260.9		182.1
Pretax reclassification adjustments for gains and other items included in Net income (loss)	$ 55.8		$ 74.7

[1] Pretax net unrealized capital gains/losses arising during the period were $260.9 and $182.1 for the six months ended June 30, 2012 and 2011, respectively.

[2] Pretax reclassification adjustments for gains (losses) and other items included in Net income (loss) were $55.8 and $74.7 for the six months ended June 30, 2012 and 2011, respectively.