Accumulated Other Comprehensive Income (Loss) by Component Schedule of Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	$ 11,969	$ 11,756
Other comprehensive income (loss) before reclassifications	262	163
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	57	21
Total stockholder's equity at end of period	12,244	11,969
Other comprehensive income (loss) after tax (expense) benefit	205	142
Reclassification from AOCI, tax	(24)	(7)
Tax (expense) benefit on other comprehensive income (loss)	(75)	(121)
Net unrealized gains (losses) on investments with OTTI losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	30	27
Other comprehensive income (loss) before reclassifications	(3)	9
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	2	6
Total stockholder's equity at end of period	25	30
Other comprehensive income (loss) after tax (expense) benefit	(5)	3
Reclassification from AOCI, tax	(1)	(3)
Tax (expense) benefit on other comprehensive income (loss)	2	(1)
Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	642	390
Other comprehensive income (loss) before reclassifications	190	290
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	82	38
Total stockholder's equity at end of period	750	642
Other comprehensive income (loss) after tax (expense) benefit	108	252
Reclassification from AOCI, tax	(38)	(16)
Tax (expense) benefit on other comprehensive income (loss)	(68)	(117)
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(647)	(648)
Other comprehensive income (loss) before reclassifications	(25)	(22)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(27)	(23)
Total stockholder's equity at end of period	(645)	(647)
Other comprehensive income (loss) after tax (expense) benefit	2	1
Reclassification from AOCI, tax	15	12
Tax (expense) benefit on other comprehensive income (loss)	(9)	(3)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(198)	(84)
Other comprehensive income (loss) before reclassifications	100	(114)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	0	0
Total stockholder's equity at end of period	(98)	(198)
Other comprehensive income (loss) after tax (expense) benefit	100	(114)
Reclassification from AOCI, tax	0	0
Tax (expense) benefit on other comprehensive income (loss)	0	0
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(173)	(315)
Total stockholder's equity at end of period	$ 32	$ (173)