Employee Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Qualified Pension Plan
Net periodic cost consists of:
Service cost	$ 28	$ 28
Interest cost	46	43
Expected return on plan assets	(72)	(76)
Amortization of prior service credit	1
Net periodic cost/(benefit)	3	(5)
Nonqualified Pension Plan
Net periodic cost consists of:
Service cost	1	1
Interest cost	2	2
Amortization of actuarial losses	1	1
Net periodic cost/(benefit)	4	4
Postretirement Benefits
Net periodic cost consists of:
Service cost	1	1
Interest cost	3	3
Expected return on plan assets	(1)	(1)
Net periodic cost/(benefit)	$ 3	$ 3