Derivatives and Hedging Activites (Option Pay/Rec) (Details 3) $ in Millions	Mar. 31, 2017 USD ($)
Summary of Option Premiums Payable and Receivable
Premiums payable	$ 1,759
Premiums receivable	764
2017 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	223	[1]
Premiums receivable	70	[1]
2018 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	229
Premiums receivable	131
2019 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	275
Premiums receivable	172
2020 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	196
Premiums receivable	99
2021 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	186
Premiums receivable	108
2022-2027 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	650
Premiums receivable	$ 184

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