Commitments and Contingencies (Details) (USD $) In Millions	Jun. 30, 2011
Indemnity
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	$ 43
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	12
Indemnity | Real estate
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	13
Exchange
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	434
Exchange | Private equity
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	193
Exchange | Mezzanine debt
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	124
Exchange | Real estate
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	$ 117