Employee Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Qualified Pension Plan
Net periodic cost consists of:
Service cost	$ 29	$ 30	$ 57	$ 58
Interest cost	47	42	93	85
Expected return on plan assets	(71)	(77)	(143)	(153)
Amortization of prior service credit	1	1	2	1
Amortization of actuarial losses	3		3
Net periodic cost/(benefit)	9	(4)	12	(9)
Nonqualified Pension Plan
Net periodic cost consists of:
Service cost			1	1
Interest cost	3	3	5	5
Amortization of actuarial losses	1	1	2	2
Net periodic cost/(benefit)	4	4	8	8
Postretirement Benefits
Net periodic cost consists of:
Service cost	1	1	2	2
Interest cost	4	3	7	6
Expected return on plan assets	(2)	(2)	(3)	(3)
Net periodic cost/(benefit)	$ 3	$ 2	$ 6	$ 5