Derivatives and Hedging Activites (Option Pay/Rec) (Details 3) $ in Millions	Mar. 31, 2019 USD ($)
Summary of Option Premiums Payable and Receivable
Premiums payable	$ 1,502
Premiums receivable	661
2019 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	288	[1]
Premiums receivable	140	[1]
2020 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	216
Premiums receivable	135
2021 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	187
Premiums receivable	127
2022 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	239
Premiums receivable	200
2023 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	141
Premiums receivable	42
2024-2028 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	431
Premiums receivable	$ 17

[1] 2019 amounts represent the amounts payable and receivable for the period from April 1, 2019 to December 31, 2019.