Investment Securities (Non-agency Mortgage-backed Securities) (Details) (Fair Value, USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012		Dec. 31, 2011
Investment securities
Fair value investments	$ 6,565.5	[1],[2]	$ 6,950.7	[1],[2]	$ 6,571.9	[3],[4]	$ 7,500.8	[3],[4]
Residential Mortgage Backed Securities
Investment securities
Fair value investments	133.6		160.6
Commercial Mortgage Backed Securities
Investment securities
Fair value investments	300.3		334.1
Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	433.9		494.7
Securities Issued in 2004 [Member] | Residential Mortgage Backed Securities
Investment securities
Fair value investments	13.2
Securities Issued in 2004 [Member] | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	0
Securities Issued in 2004 [Member] | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	13.2
Securities Issued in 2005 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	32.6
Securities Issued in 2005 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	0
Securities Issued in 2005 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	32.6
Securities Issued In 2006 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	10.7
Securities Issued In 2006 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	8.7
Securities Issued In 2006 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	19.4
Securities Issued In 2007 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	3.8
Securities Issued In 2007 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	11.6
Securities Issued In 2007 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	15.4
Securities Issued In 2008 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	0
Securities Issued In 2008 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	34.9
Securities Issued In 2008 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	34.9
Securities Issued In 2010 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	35.4
Securities Issued In 2010 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	12.4
Securities Issued In 2010 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	47.8
Securities Issued In 2011 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	0
Securities Issued In 2011 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	38.2
Securities Issued In 2011 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	38.2
Securities Issued in 2012 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	0
Securities Issued in 2012 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	118.6
Securities Issued in 2012 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	118.6
Securities Issued in 2013 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	37.9
Securities Issued in 2013 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	75.9
Securities Issued in 2013 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	$ 113.8

[1] Carrying value includes $260.8 that is classified as assets held for sale relating to discontinued operations.

[2] Excludes carrying value of $34.2 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.1) related to forward contracts.

[3] Carrying value includes $111.8 that is classified as assets held for sale relating to discontinued operations.

[4] Excludes carrying value of $33.0 and $34.0 at January 1, 2012 and June 30, 2012 associated with other long-term investment limited partnerships accounted for using the equity method.