Retirement and Benefit Plans - Net Periodic Benefit Cost and Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of net periodic benefit cost:
Interest cost	$ 6	$ 7	$ 7
Expected return on assets	(4)	(8)	(11)
Amortization of net actuarial loss	6	6	6
Settlement	3	3	3
Net periodic benefit cost	11	8	5
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net actuarial loss (gain)	12	5	(1)
Amortization of net actuarial loss	(6)	(6)	(6)
Settlement	(3)	(3)	(3)
Total recognized in other comprehensive income	3	(4)	(10)
Total recognized in net periodic benefit cost and other comprehensive income	$ 14	$ 4	$ (5)