Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of the change in the amount of unrecognized tax benefits
Balance – beginning of year	$ 7	$ 0	$ 0
Increase for tax positions taken in a prior year	0	4	0
Decrease for tax positions taken in a prior year	0	0	0
Increase for tax positions taken in the current year	3	3	0
Decrease for tax positions taken in the current year	0	0	0
Decrease for settlements	0	0	0
Reductions due to lapse of statute of limitations	0	0	0
Balance – end of year	10	7	0
Deferred assets
Unearned premium reserves	819	796
Pension	294	236
Accrued compensation	203	189
Discount on loss reserves	188	203
Difference in tax bases of invested assets	78	202
Other postretirement benefits	64	76
Other assets	118	137
Total deferred assets	1,764	1,839
Deferred liabilities
DAC	(1,211)	(1,157)
Unrealized net capital gains	(529)	(303)
Life and annuity reserves	(324)	(260)
Other liabilities	(187)	(209)
Total deferred liabilities	(2,251)	(1,929)
Net deferred liability	(487)	(90)
Components of income tax expense (benefit)
Current	654	1,033	1,123
Deferred	223	78	263
Total income tax expense	877	1,111	1,386
Net operating loss carryforward	42
Income tax paid	359	1,070	$ 1,070
Current income tax payable	$ 135
Current income tax receivable		$ 59
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation
Statutory federal income tax rate	35.00%	35.00%	35.00%
Tax-exempt income	(1.20%)	(1.00%)	(0.90%)
Tax credits	(1.20%)	(0.90%)	(0.70%)
Sale of subsidiary	0.00%	0.00%	(0.90%)
Other	(0.70%)	0.80%	0.20%
Effective income tax rate (as a percent)	31.90%	33.90%	32.70%
Accounting Standards Update 2014-01
Components of income tax expense (benefit)
Total income tax expense		$ 45