Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Income taxes
Net deferred tax liability, consolidated	$ 371
Net deferred tax asset	39	37
Net deferred tax liability	410	365
Deferred tax asset valuation allowance	0
Indemnity
Income taxes
Net deferred tax asset	39	37
Net deferred tax liability	0	0
Effective tax rate when investment related permanent tax differences are excluded (as a percent)	35.00%
Exchange
Income taxes
Net deferred tax asset	0	0
Net deferred tax liability	$ 410	$ 365
Effective tax rate when investment related permanent tax differences are excluded (as a percent)	35.00%
Minimum | Indemnity
Income taxes
Percent of total permanent tax differences related to investment revenues (as a percent)	98.00%
Minimum | Exchange
Income taxes
Percent of total permanent tax differences related to investment revenues (as a percent)	98.00%