Investment Securities (Non-agency Mortgage-backed Securities) (Details) (USD $)	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012		Dec. 31, 2011
Investment securities
Fair value investments	$ 1.3
Fair Value
Investment securities
Fair value investments	6,622,400,000	[1],[2]	6,950,700,000	[1],[2]	6,709,100,000	[3],[4]	7,500,800,000	[3],[4]
Fair Value | Residential Mortgage Backed Securities
Investment securities
Fair value investments	130,600,000		160,600,000
Fair Value | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	296,400,000		334,100,000
Fair Value | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	427,000,000		494,700,000
Fair Value | Securities Issued in 2004 [Member] | Residential Mortgage Backed Securities
Investment securities
Fair value investments	12,600,000
Fair Value | Securities Issued in 2004 [Member] | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	0
Fair Value | Securities Issued in 2004 [Member] | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	12,600,000
Fair Value | Securities Issued in 2005 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	29,800,000
Fair Value | Securities Issued in 2005 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	0
Fair Value | Securities Issued in 2005 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	29,800,000
Fair Value | Securities Issued In 2006 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	10,700,000
Fair Value | Securities Issued In 2006 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	8,700,000
Fair Value | Securities Issued In 2006 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	19,400,000
Fair Value | Securities Issued In 2007 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	3,000,000
Fair Value | Securities Issued In 2007 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	11,500,000
Fair Value | Securities Issued In 2007 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	14,500,000
Fair Value | Securities Issued In 2008 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	0
Fair Value | Securities Issued In 2008 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	30,800,000
Fair Value | Securities Issued In 2008 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	30,800,000
Fair Value | Securities Issued In 2010 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	38,600,000
Fair Value | Securities Issued In 2010 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	12,100,000
Fair Value | Securities Issued In 2010 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	50,700,000
Fair Value | Securities Issued In 2011 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	0
Fair Value | Securities Issued In 2011 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	34,600,000
Fair Value | Securities Issued In 2011 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	34,600,000
Fair Value | Securities Issued in 2012 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	0
Fair Value | Securities Issued in 2012 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	116,300,000
Fair Value | Securities Issued in 2012 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	116,300,000
Fair Value | Securities Issued in 2013 | Residential Mortgage Backed Securities
Investment securities
Fair value investments	35,900,000
Fair Value | Securities Issued in 2013 | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	82,400,000
Fair Value | Securities Issued in 2013 | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	$ 118,300,000

[1] Carrying value includes $239.7 that is classified as assets held for sale relating to discontinued operations.

[2] Excludes carrying value of $26.9 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 September 30, 2012 associated with other long-term investment limited partnerships accounted for using the equity method.