Derivatives and Hedging Activities (Option Pay/Rec) (Details 3) $ in Millions	Dec. 31, 2017 USD ($)
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	$ 1,706
Premiums receivable for derivative option contracts	718
2018 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	233
Premiums receivable for derivative option contracts	131
2019 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	296
Premiums receivable for derivative option contracts	171
2020 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	217
Premiums receivable for derivative option contracts	100
2021 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	187
Premiums receivable for derivative option contracts	109
2022 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	250
Premiums receivable for derivative option contracts	148
2023-2027 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	523
Premiums receivable for derivative option contracts	$ 59