Commitments and Contingencies Commitments and Contingencies Leases (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jun. 30, 2009 New York Office Space [Member] tenant	Jun. 30, 2008 New York Office Space [Member]
Commitments and Contingencies
Term of lease agreement for New York office space (in years)					5 years
Future minimum annual payments for the first twelve month period					$ 5
Future minimum annual payments for subsequent twelve month periods					6
Number of tenants to whom property is sub-leased				2
Total minimum annual sublease rentals				4
Rent Expense	10.0	10.7	11.4
Future Minimum Payments Due
2013	14
2014	8
2015	8
2016	8
2017	8
Thereafter	66
Total	$ 112