Derivative Financial Instruments - Dealer Counterparties and Central Clearing Parties (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Unsecured positions in a net gain with counterparties after collateral postings	$ 4,015	$ 2,035
Dealer Counterparties
Credit Derivatives [Line Items]
Cash and other collateral received from counterparties	1,467	514
Derivatives in a net gain position secured by collateral received	1,581	615
Unsecured positions in a net gain with counterparties after collateral postings	114	101
Cash collateral posted	1,005	1,255
Derivatives in a net loss position	1,052	1,300
Additional collateral that would have been posted had the Company's credit ratings dropped below investment grade	13	12
Central Clearing Parties
Credit Derivatives [Line Items]
Derivatives in a net gain position secured by collateral received	5	0
Cash collateral posted	220	30
Derivatives in a net loss position	199	31
Securities pledged to central counterparties clearing	$ 663	$ 513