Derivatives and Hedging Activites (Option Pay/Rec) (Details 4) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Summary of Option Premiums Payable and Receivable
Premiums payable	$ 2,017
Premiums receivable	520
Current Year [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	311	[1]
Premiums receivable	57	[1]
2015 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	334
Premiums receivable	68
2016 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	274
Premiums receivable	69
2017 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	205
Premiums receivable	93
2018 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	259
Premiums receivable	87
2019-2027 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	634
Premiums receivable	$ 146

[1] 2015 amounts represent the amounts payable and receivable for the period from April 1, 2015 to December 31, 2015.