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
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 454	$ 407
Reported in Net realized investment gains (losses)	4
Reported in Net investment income	0
Reported in Other comprehensive income	(5)	4
Total realized and unrealized investment gains (losses)	(1)	11
Purchases	30	44
Sales	(72)	(17)
Settlements	(8)	(25)
Transfers into Level 3	5	28
Transfers out of Level 3	(10)	(5)
Balance at end of period	398	443
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	(2)	0
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	98	130
Reported in Net realized investment gains (losses)	(1)
Reported in Net investment income	0
Reported in Other comprehensive income	0	1
Total realized and unrealized investment gains (losses)	(1)	1
Purchases	0	5
Sales	0	(1)
Settlements	(2)	(14)
Transfers into Level 3	5	0
Transfers out of Level 3	0	0
Balance at end of period	100	121
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	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
Reported in Net realized investment gains (losses)	0
Reported in Net investment income	0
Reported in Other comprehensive income	0	0
Total realized and unrealized investment gains (losses)	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
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
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	335	199
Reported in Net realized investment gains (losses)	7
Reported in Net investment income	0
Reported in Other comprehensive income	(5)	2
Total realized and unrealized investment gains (losses)	2	2
Purchases	30	38
Sales	(72)	0
Settlements	(6)	(6)
Transfers into Level 3	0	28
Transfers out of Level 3	(10)	(5)
Balance at end of period	279	256
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	20	19
Reported in Net realized investment gains (losses)	(2)
Reported in Net investment income	0
Reported in Other comprehensive income	0	1
Total realized and unrealized investment gains (losses)	(2)	1
Purchases	0	1
Sales	0	(2)
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at end of period	18	19
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	$ (2)	0
Derivative financial instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		0
Reported in Other comprehensive income		0
Total realized and unrealized investment gains (losses)		1
Purchases		0
Sales		(1)
Settlements		0
Transfers into Level 3		0
Transfers out of Level 3		0
Balance at end of period		0
Life settlement contracts, included in Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		58
Reported in Other comprehensive income		0
Total realized and unrealized investment gains (losses)		6
Purchases		0
Sales		(13)
Settlements		(5)
Transfers into Level 3		0
Transfers out of Level 3		0
Balance at end of period		46
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)		0
Net Realized Investment Gain (Losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		1
Net Realized Investment Gain (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
Net Realized Investment Gain (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
Net Realized Investment Gain (Losses) | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0
Net Realized Investment Gain (Losses) | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0
Net Realized Investment Gain (Losses) | Derivative financial instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		1
Net Realized Investment Gain (Losses) | Life settlement contracts, included in Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		0
Other Revenues
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		6
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
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
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
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
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
Other Revenues | Life settlement contracts, included in Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net realized investment gains (losses)		$ 6