Certain Employee Benefit and Stock Based Compensation Plans (Net Periodic Pension and Postretirement Benefits Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 26	$ 27
Interest cost	46	44
Expected return on plan assets	(70)	(74)
Amortization of prior service cost/(credit)	(2)	(2)
Amortization of actuarial losses	11	7
Net periodic cost/(benefit)	11	2
Nonqualified Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	3	3
Amortization of actuarial losses	1	2
Net periodic cost/(benefit)	4	5
Postretirement Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	4	4
Expected return on plan assets	(1)
Net periodic cost/(benefit)	$ 4	$ 5