Employee Benefit Plans (Net Periodic Pension and Postretirement Benefits Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 26	$ 27	$ 77	$ 80
Interest cost	46	44	139	133
Expected return on plan assets	(70)	(75)	(211)	(223)
Amortization of prior service cost/(credit)	(2)	(2)	(5)	(6)
Amortization of actuarial losses	12	8	34	23
Net periodic cost/(benefit)	12	2	34	7
Nonqualified Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	2	2
Interest cost	3	3	9	9
Amortization of actuarial losses	1	2	3	5
Net periodic cost/(benefit)	5	6	14	16
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	4	4
Interest cost	4	4	11	11
Expected return on plan assets	(1)		(3)
Amortization of prior service cost/(credit)		(1)	(1)	(1)
Net periodic cost/(benefit)	$ 4	$ 4	$ 11	$ 14