Derivatives and Hedging Activites (Option Pay/Rec) (Details 3) $ in Millions	Mar. 31, 2016 USD ($)
Summary of Option Premiums Payable and Receivable
Premiums payable	$ 1,931
Premiums receivable	668
2016 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	252	[1]
Premiums receivable	68	[1]
2017 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	276
Premiums receivable	77
2018 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	224
Premiums receivable	131
2019 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	267
Premiums receivable	130
2020 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	199
Premiums receivable	59
2021-2027 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	713
Premiums receivable	$ 203

[1] 2016 amounts represent the amounts payable and receivable for the period from April 1, 2016 to December 31, 2016.