Derivatives (Forward Contract Collateral) (Details) (Forward Contracts, USD $) In Millions, unless otherwise specified	Jun. 30, 2013 Rating	Dec. 31, 2012
Derivative [Line Items]
Net amount of exposure after effect of collateral held	$ 41.0	$ 31.2
Uncollaterailized balance of forward currency derivatives	(0.1)	(0.1)
S and P Credit Ratings	21
A | Barclays
Derivative [Line Items]
Net amount of exposure after effect of collateral held	1.7	7.7
Uncollaterailized balance of forward currency derivatives	0	(0.1)
A | Deutsche Bank
Derivative [Line Items]
Net amount of exposure after effect of collateral held	13.1	11.1
Uncollaterailized balance of forward currency derivatives	0	0
A | JP Morgan
Derivative [Line Items]
Net amount of exposure after effect of collateral held	10.0	1.9
Uncollaterailized balance of forward currency derivatives	0.2	0
A- | Goldman Sachs
Derivative [Line Items]
Net amount of exposure after effect of collateral held	5.3	0.4
Uncollaterailized balance of forward currency derivatives	(0.1)	0
AA- | HSBC
Derivative [Line Items]
Net amount of exposure after effect of collateral held	7.3	10.1
Uncollaterailized balance of forward currency derivatives	(0.1)	0
AA- | Royal Bank of Canada
Derivative [Line Items]
Net amount of exposure after effect of collateral held	3.6	0
Uncollaterailized balance of forward currency derivatives	$ (0.1)	$ 0