Derivatives and Hedging Activities (Option Pay/Rec) (Details 3) $ in Millions	Dec. 31, 2016 USD ($)
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	$ 1,790
Premiums receivable for derivative option contracts	717
2017 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	270
Premiums receivable for derivative option contracts	77
2018 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	227
Premiums receivable for derivative option contracts	130
2019 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	273
Premiums receivable for derivative option contracts	171
2020 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	195
Premiums receivable for derivative option contracts	99
2021 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	186
Premiums receivable for derivative option contracts	107
2022-2027 [Member]
Summary of Option Premiums Payable and Receivable [Line Items]
Premiums payable for derivative option contracts	639
Premiums receivable for derivative option contracts	$ 133