Derivatives (Credit Risk on Freestanding Derivatives) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Credit Derivatives [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 3,141	$ 3,129
Estimated Fair Value of Derivatives in Net Liability Position	1,198	1,138
Accrued Investment Income Receivable	614	575
Premiums and Other Receivables, Net	12,990	12,918
Fixed Maturity Securities
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided	1,568	$ 1,414
LCH update impact [Member]
Credit Derivatives [Line Items]
Derivative Liability, Fair Value, Gross Liability	77
Accrued Investment Income Receivable	2
Premiums and Other Receivables, Net	$ 75