Derivative Financial Instruments - Dealer Counterparties and Central Clearing Parties (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Unsecured positions in a net gain with counterparties after collateral postings	$ 4,208	$ 2,035
Dealer Counterparties
Credit Derivatives [Line Items]
Cash and other collateral received from counterparties	1,196	514
Derivatives in a net gain position secured by collateral received	1,313	615
Unsecured positions in a net gain with counterparties after collateral postings	117	101
Cash collateral posted	1,306	1,255
Derivatives in a net loss position	1,371	1,300
Additional collateral that would have been posted had the Company's credit ratings dropped below investment grade	6	12
Central Clearing Parties
Credit Derivatives [Line Items]
Cash collateral posted	71	30
Derivatives in a net loss position	24	31
Securities pledged to central counterparties clearing	$ 656	$ 513