Derivatives and Hedging Activites (Option Pay/Rec) (Details 3) $ in Millions	Jun. 30, 2017 USD ($)
Summary of Option Premiums Payable and Receivable
Premiums payable	$ 1,719
Premiums receivable	732
2017 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	148	[1]
Premiums receivable	39	[1]
2018 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	231
Premiums receivable	131
2019 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	293
Premiums receivable	171
2020 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	207
Premiums receivable	100
2021 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	187
Premiums receivable	108
2022-2027 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	653
Premiums receivable	$ 183

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