Contingencies, Commitments and Guarantees (Commitments - Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Mortgage Loan Commitments
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet commitments	$ 388	$ 335
Commitments to Fund Partnership Investments and Private Corporate Bond Investments
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet commitments	$ 1,400	1,300
Affiliated Entity | Secured Demand Notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet commitments		20
Fair value of collateral transferred to custody accounts to secure certain demand notes		$ 25