Subsequent Events (Details) - USD ($)		3 Months Ended	12 Months Ended
	Jan. 18, 2018	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 12, 2018
Subsequent Event [Line Items]
Reinsurance ceded			$ 1,485,000,000	$ 1,413,000,000	$ 1,311,000,000
Subsequent Event [Member] | Senior Notes, 3.80%, Due 2023, Second Issuance [Member]
Subsequent Event [Line Items]
Principal balance						$ 150,000,000
Interest rate						4.00%
Subsequent Event [Member] | Senior Notes, 3.80%, Due 2023 [Member]
Subsequent Event [Line Items]
Principal balance						$ 500,000,000
Subsequent Event [Member] | Senior Notes, 3.80%, Due 2028 [Member]
Subsequent Event [Line Items]
Principal balance						$ 500,000,000
Interest rate						3.80%
Subsequent Event [Member] | Senior Notes, 4.35%, Due 2048 [Member]
Subsequent Event [Line Items]
Principal balance						$ 450,000,000
Interest rate						4.35%
LNL [Member] | Liberty Transaction [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Consideration for aqcuisition		$ 3,300,000,000
Net investment		1,400,000,000
Purchase price		1,000,000,000
Required capital		425,000,000
Individual life and annutiy value paid		410,000,000
Excess capital		1,200,000,000
Tax items		211,000,000
Reinsurance ceded		$ 13,000,000,000
LNL [Member] | Liberty Transaction [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Acquisition agreement date	Jan. 19, 2018