Derivatives and Hedging Activites (Option Pay/Rec) (Details 3) $ in Millions	Sep. 30, 2017 USD ($)
Summary of Option Premiums Payable and Receivable
Premiums payable	$ 1,768
Premiums receivable	720
2017 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	98	[1]
Premiums receivable	26	[1]
2018 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	232
Premiums receivable	131
2019 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	295
Premiums receivable	171
2020 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	217
Premiums receivable	100
2021 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	187
Premiums receivable	109
2022-2027 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	739
Premiums receivable	$ 183

[1] 2017 amounts represent the amounts payable and receivable for the period from October 1, 2017 to December 31, 2017.