Derivative Financial Instruments - Dealer Counterparties and Central Clearing Parties (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Credit Derivatives [Line Items]
Cash collateral received from counterparties		$ 53
Unsecured positions in a net gain with counterparties after collateral postings	$ 2,035
Cash collateral posted		82
Dealer Counterparties
Credit Derivatives [Line Items]
Cash collateral received from counterparties	514	56
Derivatives in a net gain position secured by collateral received	615	55
Unsecured positions in a net gain with counterparties after collateral postings	101	2
Cash collateral posted	1,255	75
Derivatives in a net loss position	1,300	76
Additional collateral that would have been posted had the Company's credit ratings dropped below investment grade	12	1
Central Clearing Parties
Credit Derivatives [Line Items]
Cash collateral posted	30	17
Derivatives in a net loss position	31	8
Securities pledged to central counterparties clearing	$ 513	$ 124