Derivatives and Hedging Activites (Option Pay/Rec) (Details 3) $ in Millions	Sep. 30, 2018 USD ($)
Summary of Option Premiums Payable and Receivable
Premiums payable	$ 1,521
Premiums receivable	712
2018 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	54	[1]
Premiums receivable	31	[1]
2019 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	294
Premiums receivable	171
2020 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	216
Premiums receivable	132
2021 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	187
Premiums receivable	119
2022 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	225
Premiums receivable	200
2023-2027 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	545
Premiums receivable	$ 59

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