Summary of Investments Other Than Investments in Related Parties (Details) $ in Millions	Dec. 31, 2017 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	$ 48,824
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	51,691	[1]
Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	35,281
Summary of Investments, Other than Investments in Related Parties, Fair Value	38,151
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	38,151	[1]
US Treasury and Government [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	1,953
Summary of Investments, Other than Investments in Related Parties, Fair Value	1,944
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	1,944	[1]
US States and Political Subdivisions Debt Securities [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	648
Summary of Investments, Other than Investments in Related Parties, Fair Value	703
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	703	[1]
Foreign Government Debt [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	6,098	[2]
Summary of Investments, Other than Investments in Related Parties, Fair Value	7,621	[2]
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	7,621	[1],[2]
Public Utility, Bonds [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	2,454
Summary of Investments, Other than Investments in Related Parties, Fair Value	2,649
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	2,649	[1]
Asset-backed Securities [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	4,615
Summary of Investments, Other than Investments in Related Parties, Fair Value	4,672
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	4,672	[1]
All Other Corporate Bonds [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	19,513
Summary of Investments, Other than Investments in Related Parties, Fair Value	20,562
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	20,562	[1]
Nonredeemable Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	42
Summary of Investments, Other than Investments in Related Parties, Fair Value	40
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	40	[1]
Other Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	61
Summary of Investments, Other than Investments in Related Parties, Fair Value	60
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	60	[1]
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	103
Summary of Investments, Other than Investments in Related Parties, Fair Value	100
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	100	[1]
Mortgage Loans on Real Estate [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	4,401
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	4,401	[1]
Policy Loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	1,358
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	1,358	[1]
Funds Withheld At Interest [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	6,083
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	6,083	[1]
Short-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	93
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	93	[1]
Other Invested Assets [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	1,505
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	$ 1,505	[1]

[1] Fixed maturity securities are classified as available-for-sale and carried at fair value.

[2] Includes fixed maturities directly issued by foreign governments, supranational and foreign government-sponsored enterprises.