Derivative Financial Instruments - Dealer Counterparties and Central Clearing Parties (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Unsecured positions in a net gain with counterparties after collateral postings	$ 4,044	$ 2,035
Dealer Counterparties
Credit Derivatives [Line Items]
Cash and other collateral received from counterparties	470	514
Derivatives in a net gain position secured by collateral received	580	615
Unsecured positions in a net gain with counterparties after collateral postings	110	101
Cash collateral posted	1,365	1,255
Derivatives in a net loss position	1,415	1,300
Additional collateral that would have been posted had the Company's credit ratings dropped below investment grade	3	12
Central Clearing Parties
Credit Derivatives [Line Items]
Derivatives in a net gain position secured by collateral received	2	0
Cash collateral posted	128	30
Derivatives in a net loss position	29	31
Securities pledged to central counterparties clearing	$ 775	$ 513