Investments (Details 5) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Realized gains (losses) on investments
Net realized investment gains (losses)	$ (7.0)	$ 133.0	$ 49.0	$ 189.0
Other-than-temporary impairments on investments
Net impairment losses recognized in earnings	(2.0)	0.0	(4.0)	0.0
Indemnity
Realized gains (losses) on investments
Net realized investment gains (losses)	0.0	0.0	0.0	1.0
Other-than-temporary impairments on investments
Other -than-temporary impairments on investments		(0.1)	(0.2)	(0.1)
Portion recognized in other comprehensive income	0.0	0.0	0.0	0.0
Indemnity \| Maximum
Other-than-temporary impairments on investments
Other -than-temporary impairments on investments	(0.1)
Indemnity \| Fixed maturities
Available-for-sale securities:
Gross realized gains	0.0	0.0	0.0	0.0
Gross realized losses	0.0	0.0	0.0	0.0
Net realized gains (losses)	0.0	0.0	0.0	0.0
Indemnity \| Equity securities
Available-for-sale securities:
Gross realized gains	0.0	0.0	0.0	1.0
Gross realized losses	0.0	0.0	0.0	0.0
Net realized gains (losses)	0.0	0.0	0.0	1.0
Exchange
Realized gains (losses) on investments
Net realized investment gains (losses)	(7.0)	133.0	49.0	188.0
Other-than-temporary impairments on investments
Other -than-temporary impairments on investments	(2.0)	(0.1)	(4.0)	(0.3)
Portion recognized in other comprehensive income	0.0	0.0	0.0	0.0
Exchange \| Fixed maturities
Available-for-sale securities:
Gross realized gains	7.0	4.0	13.0	10.0
Gross realized losses	(4.0)	0.0	(8.0)	(1.0)
Net realized gains (losses)	3.0	4.0	5.0	9.0
Exchange \| Equity securities
Available-for-sale securities:
Gross realized gains	6.0	2.0	11.0	10.0
Gross realized losses	(1.0)	(1.0)	(1.0)	(2.0)
Net realized gains (losses)	5.0	1.0	10.0	8.0
Exchange \| Common stock
Trading securities:
Gross realized gains	49.0	52.0	166.0	122.0
Gross realized losses	(11.0)	(7.0)	(23.0)	(10.0)
Increases (decreases) in fair value	(53.0)	83.0	(109.0)	59.0
Net realized gains (losses)	$ (15.0)	$ 128.0	$ 34.0	$ 171.0

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