Employee Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Qualified Plan [Member]
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	$ 1	$ 1
Defined Benefit Plan, Interest Cost	8	6
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(4)	(6)
Defined Benefit Plan, Amortization of Gain (Loss)	6	6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	11	7
Nonqualified Plan [Member]
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	0	0
Defined Benefit Plan, Interest Cost	1	1
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	0	0
Defined Benefit Plan, Amortization of Gain (Loss)	1	1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ 2	$ 2