Employee Benefit Plans (Net Periodic Pension and Postretirement Benefits Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 25	$ 26	$ 51	$ 53
Interest cost	47	45	93	89
Expected return on plan assets	(71)	(74)	(141)	(148)
Amortization of prior service cost/(credit)	(1)	(2)	(3)	(4)
Amortization of actuarial losses	11	8	22	15
Net periodic cost/(benefit)	11	3	22	5
Nonqualified Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	1	1
Interest cost	3	3	6	6
Amortization of actuarial losses	1	1	2	3
Net periodic cost/(benefit)	5	5	9	10
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2	3	3
Interest cost	3	3	7	7
Expected return on plan assets	(1)		(2)
Amortization of prior service cost/(credit)	(1)		(1)
Net periodic cost/(benefit)	$ 3	$ 5	$ 7	$ 10