Fair Value of Assets and Liabilities Fair Value of Assets and Liabilities (Transfers Between Level 1 and Level 2) (Details) - Separate account assets - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assets Level1 To Level2 Transfers	$ 111	$ 86
Fair Value Assets Level2 to Level1 Transfers	$ 207	$ 40

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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