Managed Investment Entities - Narrative (Details) $ in Millions	1 Months Ended		3 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) collateralizedloanobligation	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Variable Interest Entity [Line Items]
Percentage of investment of most subordinate debt tranche, Minimum			15.00%
Percentage of investment of most subordinate debt tranche, Maximum			60.90%
Number of collateralized loan obligation entities | collateralizedloanobligation			16
Proceeds received by subsidiaries related to sales and redemptions of managed investment entities liabilities			$ 17	$ 4
Number of collateralized loan obligation entities substantially liquidated, during the period | collateralizedloanobligation			1
Difference between aggregate unpaid principal balance and fair value of CLOs' fixed maturity investments	$ 38		$ 38		$ 55
Difference between aggregate unpaid principal balance and carrying value of CLOs' debt	143		143		118
Carrying amount of CLO loans in default	1		1		1
Aggregate unpaid principal balance of CLO loans in default	8		8		8
Variable interest entity, primary beneficiary
Variable Interest Entity [Line Items]
Aggregate fair value of investment in collateralized loan obligations	221	$ 230	221	$ 230	$ 215
New Collateralized Loan Obligation Entities
Variable Interest Entity [Line Items]
Face value of liabilities issued by managed investment entities on issuance date	463	408
Face amount of managed investment entities liabilities purchased by subsidiaries at issuance date	31	$ 24
Subordinated Debt Obligations | Variable interest entity, primary beneficiary
Variable Interest Entity [Line Items]
Aggregate fair value of investment in collateralized loan obligations	$ 136		$ 136