Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit credit	$ (29)	$ (18)	$ (18)
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.43%	4.37%
Service cost	$ 31	$ 29	29
Interest cost	80	75	78
Expected return on plan assets	(166)	(165)	(159)
Amortization of prior service (credit) cost	(19)	(19)	(19)
Amortization of net loss	34	51	43
Total other components of net benefit credit or cost	(71)	(58)	(57)
Net periodic defined benefit credit	(40)	(29)	(28)
Actual return on plan assets	$ 579	$ (167)	$ 396
Actual rate of return on plan assets, percent	24.07%	(6.21%)	16.48%
Weighted-average assumptions, discount rate, percent	4.37%	3.74%	4.23%
Weighted-average assumptions, expected long-term return on plan assets, percent	6.50%	6.50%	6.50%
Weighted-average assumptions, rate of compensation increase, percent	4.00%	3.75%	3.50%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	4.00%	4.00%
Non-Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.43%	4.37%
Service cost	$ 3	$ 2	$ 2
Interest cost	9	8	8
Expected return on plan assets	0	0	0
Amortization of prior service (credit) cost	(8)	(8)	(8)
Amortization of net loss	7	9	8
Total other components of net benefit credit or cost	8	9	8
Net periodic defined benefit credit	$ 11	$ 11	$ 10
Weighted-average assumptions, discount rate, percent	4.37%	3.74%	4.23%
Weighted-average assumptions, rate of compensation increase, percent	4.00%	3.75%	3.50%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	4.00%	4.00%
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.26%	4.26%
Service cost	$ 0	$ 0
Interest cost	2	2	$ 2
Expected return on plan assets	(3)	(3)	(3)
Amortization of net loss	1	1	1
Net periodic defined benefit credit	0	0	0
Actual return on plan assets	$ 5	$ (1)	$ 2
Actual rate of return on plan assets, percent	9.14%	(2.05%)	3.52%
Weighted-average assumptions, discount rate, percent	4.26%	3.55%	3.92%
Weighted-average assumptions, expected long-term return on plan assets, percent	5.00%	5.00%	5.00%
Health care cost trend rate assumed	6.50%	6.50%	6.50%
Rate to which the healthcare cost trend rate is assumed to decline (the ultimate trend rate), percent	4.50%	4.50%	4.50%
Defined Benefit Plan Year That Reaches Ultimate Trend Rate In Current Expense	2027	2027	2027
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2027	2027
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	6.25%	6.50%