Derivatives and Hedging Activites (Option Pay/Rec) (Details 3) $ in Millions	Mar. 31, 2018 USD ($)
Summary of Option Premiums Payable and Receivable
Premiums payable	$ 1,692
Premiums receivable	764
2018 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	192	[1]
Premiums receivable	78	[1]
2019 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	299
Premiums receivable	173
2020 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	219
Premiums receivable	132
2021 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	188
Premiums receivable	121
2022 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	253
Premiums receivable	200
2023-2027 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	541
Premiums receivable	$ 60

[1] 2018 amounts represent the amounts payable and receivable for the period from April 1, 2018 to December 31, 2018.