Employee Benefits, Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		123 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019
Qualified Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 3	$ 2	$ 9	$ 5
Interest cost	105	97	314	293
Expected return on plan assets	(142)	(160)	(426)	(481)
Amortization of net actuarial loss (gain)	37	32	111	98
Amortization of prior service credit	0	0	0	0
Settlement loss	0	0	0	0
Net periodic benefit cost (income)	3	(29)	8	(85)
Nonqualified Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0	0	0	0
Interest cost	5	5	16	16
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss (gain)	3	4	8	10
Amortization of prior service credit	0	0	0	0
Settlement loss	0	0	2	3
Net periodic benefit cost (income)	8	9	26	29
Other benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0	0	0	0
Interest cost	6	6	17	16
Expected return on plan assets	(7)	(8)	(21)	(23)
Amortization of net actuarial loss (gain)	(5)	(4)	(13)	(13)
Amortization of prior service credit	(2)	(3)	(7)	(8)
Settlement loss	0	0	0	0
Net periodic benefit cost (income)	$ (8)	$ (9)	$ (24)	$ (28)
Cash Balance Plan [Member]
Components of net periodic benefit cost [Abstract]
Net periodic benefit cost (income)					$ 0