Employee Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contribution	$ 200
Net periodic cost consists of:
Service cost		$ 29	$ 26	$ 87	$ 77
Interest cost		43	45	128	134
Expected return on plan assets		(76)	(71)	(229)	(213)
Amortization of prior service credit			(1)	1	(3)
Amortization of actuarial losses			11		33
Net periodic cost/(benefit)		(4)	10	(13)	28
Nonqualified Pension Plan
Net periodic cost consists of:
Service cost		1	1	2	2
Interest cost		2	2	7	8
Amortization of actuarial losses		1	1	3	3
Net periodic cost/(benefit)		4	4	12	13
Postretirement Benefits
Net periodic cost consists of:
Service cost		1	2	3	4
Interest cost		3	3	9	10
Expected return on plan assets		(1)	(2)	(4)	(4)
Amortization of prior service credit					(1)
Net periodic cost/(benefit)		$ 3	$ 3	$ 8	$ 9