Contracts Accounted for as Credit Derivatives - Narrative (Details) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) Counterparty	Dec. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Credit Derivatives
Net Par Outstanding	$ 6,160	$ 6,182
Credit risk derivatives, at fair value, net	(216)	(207)
Net expected loss to be paid after recoveries	$ 960	$ 1,183	$ 963	$ 1,432	$ 1,298	$ 1,303
Estimated remaining weighted average life of credit derivatives (in years)	11 years 4 months 24 days	11 years 7 months 6 days
Gross par of CDS with collateral posting requirement [Member]
Credit Derivatives
Number of counterparties | Counterparty	1