Employee Benefits, Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		120 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019
Qualified Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 3	$ 2	$ 6	$ 3
Interest cost	104	98	209	196
Expected return on plan assets	(142)	(161)	(284)	(321)
Amortization of net actuarial loss (gain)	37	33	74	66
Amortization of prior service credit	0	0	0	0
Settlement loss	0	0	0	0
Net periodic benefit cost (income)	2	(28)	5	(56)
Nonqualified Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0	0	0	0
Interest cost	5	6	11	11
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss (gain)	3	3	5	6
Amortization of prior service credit	0	0	0	0
Settlement loss	0	0	2	3
Net periodic benefit cost (income)	8	9	18	20
Other benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0	0	0	0
Interest cost	6	5	11	10
Expected return on plan assets	(7)	(8)	(14)	(15)
Amortization of net actuarial loss (gain)	(4)	(5)	(8)	(9)
Amortization of prior service credit	(3)	(2)	(5)	(5)
Settlement loss	0	0	0	0
Net periodic benefit cost (income)	$ (8)	$ (10)	$ (16)	$ (19)
Cash Balance Plan [Member]
Components of net periodic benefit cost [Abstract]
Net periodic benefit cost (income)					$ 0