Derivatives and Hedging Activities (Option Pay/Rec) (Details 3) $ in Millions	Dec. 31, 2018 USD ($)
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	$ 1,469
Premiums receivable for derivative option contracts	680
2019 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	294
Premiums receivable for derivative option contracts	170
2020 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	216
Premiums receivable for derivative option contracts	132
2021 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	187
Premiums receivable for derivative option contracts	119
2022 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	226
Premiums receivable for derivative option contracts	200
2023 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	142
Premiums receivable for derivative option contracts	42
2024-2028 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	404
Premiums receivable for derivative option contracts	$ 17