Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Assets:
Fixed-maturity securities	$ 11,168	$ 10,823
Other invested assets	173	162
Credit derivative assets	9	13
Liabilities:
Credit derivative liabilities	359	402
Investment funds, fair value	49	48
Recurring [Member]
Assets:
Other invested assets	8	8
Credit derivative assets	9	13
FG VIEs’ assets, at fair value	781	876
Other assets	114	114
Total assets carried at fair value	12,080	11,834
Liabilities:
Credit derivative liabilities	359	402
FG VIEs’ liabilities with recourse, at fair value	721	807
FG VIEs’ liabilities without recourse, at fair value	134	151
Total liabilities carried at fair value	1,214	1,360
Recurring [Member] \| Level 1 [Member]
Assets:
Other invested assets	0	0
Credit derivative assets	0	0
FG VIEs’ assets, at fair value	0	0
Other assets	26	24
Total assets carried at fair value	339	343
Liabilities:
Credit derivative liabilities	0	0
FG VIEs’ liabilities with recourse, at fair value	0	0
FG VIEs’ liabilities without recourse, at fair value	0	0
Total liabilities carried at fair value	0	0
Recurring [Member] \| Level 2 [Member]
Assets:
Other invested assets	0	0
Credit derivative assets	0	0
FG VIEs’ assets, at fair value	0	0
Other assets	28	28
Total assets carried at fair value	9,775	9,263
Liabilities:
Credit derivative liabilities	0	0
FG VIEs’ liabilities with recourse, at fair value	0	0
FG VIEs’ liabilities without recourse, at fair value	0	0
Total liabilities carried at fair value	0	0
Recurring [Member] \| Level 3 [Member]
Assets:
Other invested assets	8	8
Credit derivative assets	9	13
FG VIEs’ assets, at fair value	781	876
Other assets	60	62
Total assets carried at fair value	1,966	2,228
Liabilities:
Credit derivative liabilities	359	402
FG VIEs’ liabilities with recourse, at fair value	721	807
FG VIEs’ liabilities without recourse, at fair value	134	151
Total liabilities carried at fair value	1,214	1,360
Fixed Maturities [Member]
Assets:
Fixed-maturity securities	10,479	10,233
Fixed Maturities [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	5,622	5,432
Fixed Maturities [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	414	440
Fixed Maturities [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	1,874	1,613
Fixed Maturities [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	992	987
Fixed Maturities [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	568	583
Fixed Maturities [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	690	945
Fixed Maturities [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	319	233
Fixed Maturities [Member] \| Recurring [Member]
Assets:
Fixed-maturity securities	10,479	10,233
Fixed Maturities [Member] \| Recurring [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	5,622	5,432
Fixed Maturities [Member] \| Recurring [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	414	440
Fixed Maturities [Member] \| Recurring [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	1,874	1,613
Fixed Maturities [Member] \| Recurring [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	992	987
Fixed Maturities [Member] \| Recurring [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	568	583
Fixed Maturities [Member] \| Recurring [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	690	945
Fixed Maturities [Member] \| Recurring [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	319	233
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 1 [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member]
Assets:
Fixed-maturity securities	9,371	8,964
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	5,580	5,393
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	414	440
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	1,812	1,553
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	590	622
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	568	583
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	88	140
Fixed Maturities [Member] \| Recurring [Member] \| Level 2 [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	319	233
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member]
Assets:
Fixed-maturity securities	1,108	1,269
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	42	39
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| US government and agencies [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| Corporate securities [Member]
Assets:
Fixed-maturity securities	62	60
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| RMBS [Member]
Assets:
Fixed-maturity securities	402	365
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| CMBS [Member]
Assets:
Fixed-maturity securities	0	0
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	602	805
Fixed Maturities [Member] \| Recurring [Member] \| Level 3 [Member] \| Foreign government securities [Member]
Assets:
Fixed-maturity securities	0	0
Short-term Investments [Member]
Assets:
Fixed-maturity securities	689	590
Short-term Investments [Member] \| Recurring [Member]
Assets:
Fixed-maturity securities	689	590
Short-term Investments [Member] \| Recurring [Member] \| Level 1 [Member]
Assets:
Fixed-maturity securities	313	319
Short-term Investments [Member] \| Recurring [Member] \| Level 2 [Member]
Assets:
Fixed-maturity securities	376	271
Short-term Investments [Member] \| Recurring [Member] \| Level 3 [Member]
Assets:
Fixed-maturity securities	$ 0	$ 0

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