Fair Value Measurements (Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	$ 78	$ 55
Total gains or losses (realized/unrealized):
Included in net income	0	0
Included in other comprehensive income	0	(1)
Purchases	5	57
Sales	0	(3)
Transfers into Level 3	0	13
Transfers out of Level 3	(77)	(43)
Ending balance	6	78
Corporate Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	78	51
Total gains or losses (realized/unrealized):
Included in net income	0	0
Included in other comprehensive income	0	0
Purchases	0	57
Sales	0	(1)
Transfers into Level 3	0	13
Transfers out of Level 3	(77)	(42)
Ending balance	1	78
Taxable Fixed Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	0	1
Total gains or losses (realized/unrealized):
Included in net income	0	0
Included in other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	(1)
Ending balance	0	0
States, Municipalities and Political Subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	0
Total gains or losses (realized/unrealized):
Included in net income	0
Included in other comprehensive income	0
Purchases	5
Sales	0
Transfers into Level 3	0
Transfers out of Level 3	0
Ending balance	5	0
Nonredeemable Preferred Equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	0	3
Total gains or losses (realized/unrealized):
Included in net income	0	0
Included in other comprehensive income	0	(1)
Purchases	0	0
Sales	0	(2)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending balance	$ 0	$ 0