- Fair Value Level 3 Rollforward Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Short-term Investments [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period	$ 0	$ 60
Acquisition		0
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)		0
Other comprehensive income (loss)		0
Purchases		0
Settlements		(60)
FG VIE consolidations		0
FG VIE deconsolidations		0
Transfers into Level 3		0
Fair value at end of period		0
Change in unrealized gains/(losses) related to financial instruments held		0
FG VIEs' assets, at fair value [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period	876	1,261
Acquisition	0	0
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	37	167
Other comprehensive income (loss)	0	0
Purchases	0	0
Settlements	(147)	(629)
FG VIE consolidations	39	97
FG VIE deconsolidations	(105)	(20)
Transfers into Level 3	0	0
Fair value at end of period	700	876
Change in unrealized gains/(losses) related to financial instruments held	59	93
Other Assets and Other Invested Assets [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period	65	65
Acquisition	0	0
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	(2)	0
Other comprehensive income (loss)	0	0
Purchases	1	0
Settlements	0	0
FG VIE consolidations	0	0
FG VIE deconsolidations	0	0
Transfers into Level 3	0	0
Fair value at end of period	64	65
Change in unrealized gains/(losses) related to financial instruments held	(2)	0
Obligations of state and political subdivisions [Member] | Fixed Maturities [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period	39	8
Acquisition	0	1
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	(13)	2
Other comprehensive income (loss)	(2)	(4)
Purchases	0	33
Settlements	(2)	(1)
FG VIE consolidations	0	0
FG VIE deconsolidations	0	0
Transfers into Level 3	54	0
Fair value at end of period	76	39
Change in unrealized gains/(losses) related to financial instruments held	(2)	(4)
Corporate securities [Member] | Fixed Maturities [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period	60	71
Acquisition	0	0
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	6	(16)
Other comprehensive income (loss)	1	5
Purchases	0	0
Settlements	0	0
FG VIE consolidations	0	0
FG VIE deconsolidations	0	0
Transfers into Level 3	0	0
Fair value at end of period	67	60
Change in unrealized gains/(losses) related to financial instruments held	1	5
Residential Mortgage-Backed Securities (RMBS) [Member] | Fixed Maturities [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period	365	348
Acquisition	0	20
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	27	10
Other comprehensive income (loss)	23	(13)
Purchases	42	70
Settlements	(123)	(70)
FG VIE consolidations	0	0
FG VIE deconsolidations	0	0
Transfers into Level 3	0	0
Fair value at end of period	334	365
Change in unrealized gains/(losses) related to financial instruments held	23	(15)
Asset-backed Securities [Member] | Fixed Maturities [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period	805	657
Acquisition	7	36
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	113	51
Other comprehensive income (loss)	56	116
Purchases	173	76
Settlements	(367)	(139)
FG VIE consolidations	0	0
FG VIE deconsolidations	0	0
Transfers into Level 3	0	8
Fair value at end of period	787	805
Change in unrealized gains/(losses) related to financial instruments held	123	116
FG VIEs' liabilities with recourse, at fair value [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value at beginning of period	(807)	(1,225)
MBIA UK Acquisition	0	0
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	(16)	(125)
Other comprehensive income (loss)	0	0
Purchases	0	0
Settlements	145	597
FG VIE consolidations	0	(54)
FG VIE deconsolidations	51	0
Transfers into Level 3	0	0
Fair value at end of period	(627)	(807)
Change in unrealized gains/(losses) related to financial instruments held	(11)	(12)
FG VIEs' liabilities without recourse, at fair value [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value at beginning of period	(151)	(124)
MBIA UK Acquisition	0	0
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	(6)	(18)
Other comprehensive income (loss)	0	0
Purchases	0	0
Settlements	12	14
FG VIE consolidations	(39)	(43)
FG VIE deconsolidations	54	20
Transfers into Level 3	0	0
Fair value at end of period	(130)	(151)
Change in unrealized gains/(losses) related to financial instruments held	(6)	(17)
Credit Risk Contract [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair value at beginning of period	(389)	(365)
MBIA UK Acquisition	0	(67)
Total pretax realized and unrealized gains/(losses) recorded in:
Net income (loss)	107	74
Other comprehensive income (loss)	0	0
Purchases	0	0
Settlements	13	(31)
FG VIE consolidations	0	0
FG VIE deconsolidations	0	0
Transfers into Level 3	0	0
Fair value at end of period	(269)	(389)
Change in unrealized gains (losses) related to financial instruments held	$ 96	$ (33)