Fair Value (Table of reconciliation for assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 398	$ 443	$ 454	$ 407
Reported in Net realized investment gains (losses)	(1)		3
Reported in Net investment income	0		0
Reported in Other comprehensive income	(2)	2	(7)	6
Total realized and unrealized investment gains (losses)	(3)	3	(4)	14
Purchases	43	13	73	57
Sales	(5)	(46)	(77)	(63)
Settlements	(8)	(18)	(16)	(43)
Transfers into Level 3	13	24	18	52
Transfers out of Level 3	(53)	(80)	(63)	(85)
Balance at end of period	385	339	385	339
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	(1)	0	(3)	0
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	100	121	98	130
Reported in Net realized investment gains (losses)	0		(1)
Reported in Net investment income	0		0
Reported in Other comprehensive income	(1)	0	(1)	1
Total realized and unrealized investment gains (losses)	(1)	0	(2)	1
Purchases	2	0	2	5
Sales	(5)	0	(5)	(1)
Settlements	(2)	(11)	(4)	(25)
Transfers into Level 3	0	0	5	0
Transfers out of Level 3	0	(10)	0	(10)
Balance at end of period	94	100	94	100
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0	0	0	0
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1	1	1	1
Reported in Net realized investment gains (losses)	0		0
Reported in Net investment income	0		0
Reported in Other comprehensive income	0	0	0	0
Total realized and unrealized investment gains (losses)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance at end of period	1	1	1	1
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0	0	0	0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	279	256	335	199
Reported in Net realized investment gains (losses)	0		7
Reported in Net investment income	0		0
Reported in Other comprehensive income	(1)	1	(6)	3
Total realized and unrealized investment gains (losses)	(1)	2	1	4
Purchases	41	13	71	51
Sales	0	0	(72)	0
Settlements	(6)	(7)	(12)	(13)
Transfers into Level 3	13	24	13	52
Transfers out of Level 3	(53)	(70)	(63)	(75)
Balance at end of period	273	218	273	218
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0	0	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	18	19	20	19
Reported in Net realized investment gains (losses)	(1)		(3)
Reported in Net investment income	0		0
Reported in Other comprehensive income	0	1	0	2
Total realized and unrealized investment gains (losses)	(1)	1	(3)	2
Purchases	0	0	0	1
Sales	0	(1)	0	(3)
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance at end of period	17	19	17	19
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	(1)	0	(3)	0
Derivative financial instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0	0	0	0
Reported in Net realized investment gains (losses)	0		0
Reported in Net investment income	0		0
Reported in Other comprehensive income	0	0	0	0
Total realized and unrealized investment gains (losses)	0	0	0	1
Purchases	0	0	0	0
Sales	0	0	0	(1)
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance at end of period	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	$ 0	0	$ 0	0
Life settlement contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		46		58
Reported in Other comprehensive income		0		0
Total realized and unrealized investment gains (losses)		0		6
Purchases		0		0
Sales		(45)		(58)
Settlements		0		(5)
Transfers into Level 3		0		0
Transfers out of Level 3		0		0
Balance at end of period		1		1
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)		0		0
Reported in Net realized investment gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		1		2
Reported in Net realized investment gains (losses) | Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		0
Reported in Net realized investment gains (losses) | States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		0
Reported in Net realized investment gains (losses) | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		1		1
Reported in Net realized investment gains (losses) | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		0
Reported in Net realized investment gains (losses) | Derivative financial instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		1
Reported in Net realized investment gains (losses) | Life settlement contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		0
Reported in Other revenues
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		6
Reported in Other revenues | Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		0
Reported in Other revenues | States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		0
Reported in Other revenues | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		0
Reported in Other revenues | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		0
Reported in Other revenues | Derivative financial instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0		0
Reported in Other revenues | Life settlement contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		$ 0		$ 6