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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 385	$ 339	$ 454	$ 407
Reported in Net investment income	0		0
Reported in Other comprehensive income	0	2	(7)	8
Total realized and unrealized investment gains (losses)	(1)	3	(5)	17
Purchases	122	52	195	109
Sales	0	(1)	(77)	(64)
Settlements	(29)	(24)	(45)	(67)
Transfers into Level 3	59	116	77	168
Transfers out of Level 3	(32)	0	(95)	(85)
Balance at end of period	504	485	504	485
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Net income (loss)	(1)	0	(4)	0
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Other Comprehensive Income	1		(4)
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	94	100	98	130
Reported in Net investment income	0		0
Reported in Other comprehensive income	0	1	(1)	2
Total realized and unrealized investment gains (losses)	0	2	(2)	3
Purchases	67	13	69	18
Sales	0	0	(5)	(1)
Settlements	(3)	(11)	(7)	(36)
Transfers into Level 3	30	15	35	15
Transfers out of Level 3	0	0	0	(10)
Balance at end of period	188	119	188	119
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Net income (loss)	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Other Comprehensive Income	0		(2)
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 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	(1)	0	(1)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance at end of period	0	1	0	1
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Net income (loss)	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Other Comprehensive Income	0		0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	273	218	335	199
Reported in Net investment income	0		0
Reported in Other comprehensive income	0	1	(6)	4
Total realized and unrealized investment gains (losses)	(2)	1	(1)	5
Purchases	55	39	126	90
Sales	0	0	(72)	0
Settlements	(25)	(13)	(37)	(26)
Transfers into Level 3	29	101	42	153
Transfers out of Level 3	(32)	0	(95)	(75)
Balance at end of period	298	346	298	346
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Net income (loss)	(2)	0	(2)	0
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Other Comprehensive Income	1		(2)
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	17	19	20	19
Reported in Net investment income	0		0
Reported in Other comprehensive income	0	0	0	2
Total realized and unrealized investment gains (losses)	1	0	(2)	2
Purchases	0	0	0	1
Sales	0	0	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	18	19	18	19
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Net income (loss)	1	0	(2)	0
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Other Comprehensive Income	0		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 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 held recognized in Net income (loss)	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held recognized in Other Comprehensive Income	0		0
Life settlement contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		1		58
Reported in Other comprehensive income		0		0
Total realized and unrealized investment gains (losses)		0		6
Purchases		0		0
Sales		(1)		(59)
Settlements		0		(5)
Transfers into Level 3		0		0
Transfers out of Level 3		0		0
Balance at end of period		0		0
Unrealized gains (losses) on Level 3 assets and liabilities held 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)	1	2	3
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	1	(1)	1
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	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)	(2)	0	5	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)	1	0	(2)	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	0	$ 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