Commitments and Contingencies (Details) (USD $) In Millions	Sep. 30, 2011
Indemnity
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	$ 41
Indemnity | Private equity
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	18
Indemnity | Mezzanine debt
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	11
Indemnity | Real estate
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	12
Exchange
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	392
Exchange | Private equity
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	176
Exchange | Mezzanine debt
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	109
Exchange | Real estate
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	$ 107