Accumulated Other Comprehensive Income (Loss) by Component Schedule of Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	$ 11,217
Other comprehensive income (loss) before reclassifications	541	$ (412)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(13)	4
Other comprehensive income (loss) after tax (expense) benefit	554	(416)
Total stockholder's equity at end of period	11,455	11,425
Reclassification from AOCI, tax	3	(1)
Tax (expense) benefit on other comprehensive income (loss)	(144)	108
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	16	30
Other comprehensive income (loss) before reclassifications	4	(10)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	0	(1)
Other comprehensive income (loss) after tax (expense) benefit	4	(9)
Total stockholder's equity at end of period	20	21
Reclassification from AOCI, tax	0	0
Tax (expense) benefit on other comprehensive income (loss)	(1)	2
Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	61	859
Other comprehensive income (loss) before reclassifications	521	(414)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(5)	15
Other comprehensive income (loss) after tax (expense) benefit	526	(429)
Total stockholder's equity at end of period	587	430
Reclassification from AOCI, tax	1	(4)
Tax (expense) benefit on other comprehensive income (loss)	(141)	109
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(775)	(775)
Other comprehensive income (loss) before reclassifications	(1)	0
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(8)	(10)
Other comprehensive income (loss) after tax (expense) benefit	7	10
Total stockholder's equity at end of period	(768)	(765)
Reclassification from AOCI, tax	2	3
Tax (expense) benefit on other comprehensive income (loss)	(2)	(3)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(180)	(98)
Other comprehensive income (loss) before reclassifications	17	12
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	0	0
Other comprehensive income (loss) after tax (expense) benefit	17	12
Total stockholder's equity at end of period	(163)	(86)
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	(878)	16
Total stockholder's equity at end of period	$ (324)	$ (400)