Derivatives and Hedging Activities (Option Pay/Rec) (Details) $ in Millions	Mar. 31, 2020 USD ($)
Summary of option premiums payable and receivable
Premiums payable	$ 1,066
Premiums receivable	423
2020 [Member]
Summary of option premiums payable and receivable
Premiums payable	138	[1]
Premiums receivable	38	[1]
2021 [Member]
Summary of option premiums payable and receivable
Premiums payable	152
Premiums receivable	112
2022 [Member]
Summary of option premiums payable and receivable
Premiums payable	203
Premiums receivable	198
2023 [Member]
Summary of option premiums payable and receivable
Premiums payable	126
Premiums receivable	58
2024 [Member]
Summary of option premiums payable and receivable
Premiums payable	70
Premiums receivable	10
2025-2028 [Member]
Summary of option premiums payable and receivable
Premiums payable	377
Premiums receivable	$ 7

[1] 2020 amounts represent the amounts payable and receivable for the period from April 1, 2020 to December 31, 2020.