Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Indemnity
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	$ 30
Indemnity | Private equity
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	14
Indemnity | Mezzanine debt
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	10
Indemnity | Real estate
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	6
Exchange
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	393
Exchange | Private equity
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	142
Exchange | Mezzanine debt
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	163
Exchange | Real estate
Contractual commitments
Maximum contractual commitment to invest in limited partnerships	$ 88