Fair Value Measurements - Measured Under Certain Conditions (Details) - Fair Value Inputs Level 3 [Member] - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Impaired [Line Items]
Realized investment losses on impaired real estate, partnership entities, and commercial mortgage loans, after-tax	$ 2	$ 3
Maximum [Member]
Financing Receivable, Impaired [Line Items]
Impaired real estate, partnership entities, and commercial mortgage loans as a percent of total investments	1.00%	1.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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