Investing Activities Other than Temporary Impairment, Credit Losses Recognized in Earnings (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Credit Losses Recognized in Earnings on Available-for-Sale Debt Securities for which a Portion of the OTTI Loss was Recognized in OCI: ($ in millions)
Balance, beginning of period	$ (17.8)		$ (21.3)		$ (19.9)
Add: Credit losses on securities not previously impaired	(0.3)	[1]	(1.4)	[1]	(1.0)	[1]
Add: Credit losses on securities previously impaired	(0.8)	[1]	(1.2)	[1]	(1.4)	[1]
Less: Credit losses on securities impaired due to intent to sell	0		0		0
Less: Credit losses on securities sold	0.3		6.1		1.0
Less: Increases in cash flows expected on previously impaired securities	0		0		0
Balance, end of period	$ (18.6)		$ (17.8)		$ (21.3)

[1] Additional credit losses on securities for which a portion of the OTTI loss was recognized in AOCI are included within net OTTI losses recognized in earnings on the statements of income and comprehensive income.