Income Taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of the change in the amount of unrecognized tax benefits
Balance at beginning of period	$ 25	$ 25	$ 22
Increase for tax positions taken in a prior year			1
Increase for tax positions taken in the current year			2
Balance at end of period	25	25	25
Reduction of unrecognized tax benefit liability, reasonably possible in next twelve months	25
Deferred assets
Unearned premium reserves	666	656
Difference in tax bases of invested assets	353	564
Discount on loss reserves	280	315
Pension	278	255
Other postretirement benefits	218	188
Accrued compensation	212	213
Alternative minimum tax credit carryforward	165	255
Net operating loss carryforwards	64	203
Life and annuity reserves		10
Other assets	55	84
Total deferred assets	2,291	2,743
Valuation allowance		(67)
Net deferred assets	2,291	2,676
Deferred liabilities
Unrealized net capital gains	(1,527)	(757)
DAC	(917)	(897)
Life and annuity reserves	(130)
Other intangible assets	(107)	(142)
Other liabilities	(207)	(158)
Total deferred liabilities	(2,888)	(1,954)
Net deferred (liability) asset	(597)	722
Net operating loss carryforward	182
Alternative minimum tax credit carryforward	165
Components of income tax expense (benefit)
Current	295	14	133
Deferred	705	158	56
Total income tax expense	1,000	172	189
Income tax refund, received			8
Income tax paid	280	32
Income tax receivable	$ 157	$ 157
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation
Statutory federal income tax rate (as a percent)	35.00%	35.00%	35.00%
Tax-exempt income (as a percent)	(3.00%)	(13.60%)	(16.10%)
Tax credits (as a percent)	(1.40%)	(2.10%)	(0.50%)
Dividends received deduction (as a percent)	(0.50%)	(1.80%)	(1.50%)
Adjustment to prior year tax liabilities (as a percent)	(0.10%)	(0.80%)	(0.20%)
Other (as a percent)	0.30%	1.20%	0.50%
Effective income tax rate (as a percent)	30.30%	17.90%	17.20%