Managed Investment Entities - Narrative (Details) $ in Millions	1 Months Ended		9 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) collateralizedloanobligation	Sep. 30, 2017 USD ($) collateralizedloanobligation	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			15
Face amount of managed investment entities liabilities purchased by subsidiaries after issuance date				$ 58
Amount paid by subsidiaries to purchase managed investment entities liabilities after issuance date				58
Proceeds received by subsidiaries related to sales and redemptions of managed investment entities liabilities			$ 45	$ 86
Number of collateralized loan obligation entities substantially liquidated, during the period | collateralizedloanobligation			1	2
Difference between aggregate unpaid principal balance and fair value of CLOs' fixed maturity investments			$ 45		$ 55
Difference between aggregate unpaid principal balance and carrying value of CLOs' debt			160		118
Carrying amount of CLO loans in default			1		1
Aggregate unpaid principal balance of CLO loans in default			8		8
Variable interest entity, primary beneficiary
Variable Interest Entity [Line Items]
Aggregate fair value of investment in collateralized loan obligations			191	$ 261	$ 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			$ 133