Retirement and Benefit Plans - Plan Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure
Plan assets	$ 173	$ 175
Cash equivalents
Defined Benefit Plan Disclosure
Plan assets	4	14
Mutual and exchange-traded funds
Defined Benefit Plan Disclosure
Plan assets	68	76
Debt securities
Defined Benefit Plan Disclosure
Plan assets	101	85
U.S. Treasury and federal agencies securities
Defined Benefit Plan Disclosure
Plan assets	63	63
Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Plan assets	1	1
Asset-backed securities and other debt securities
Defined Benefit Plan Disclosure
Plan assets	37	21
Level 1
Defined Benefit Plan Disclosure
Plan assets	129	147
Level 1 | Cash equivalents
Defined Benefit Plan Disclosure
Plan assets	4	14
Level 1 | Mutual and exchange-traded funds
Defined Benefit Plan Disclosure
Plan assets	68	76
Level 1 | Debt securities
Defined Benefit Plan Disclosure
Plan assets	57	57
Level 1 | U.S. Treasury and federal agencies securities
Defined Benefit Plan Disclosure
Plan assets	57	57
Level 1 | Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 1 | Asset-backed securities and other debt securities
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 2
Defined Benefit Plan Disclosure
Plan assets	44	28
Level 2 | Cash equivalents
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 2 | Mutual and exchange-traded funds
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 2 | Debt securities
Defined Benefit Plan Disclosure
Plan assets	44	28
Level 2 | U.S. Treasury and federal agencies securities
Defined Benefit Plan Disclosure
Plan assets	6	6
Level 2 | Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Plan assets	1	1
Level 2 | Asset-backed securities and other debt securities
Defined Benefit Plan Disclosure
Plan assets	37	21
Level 3
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 3 | Cash equivalents
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 3 | Mutual and exchange-traded funds
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 3 | Debt securities
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 3 | U.S. Treasury and federal agencies securities
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 3 | Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Plan assets	0	0
Level 3 | Asset-backed securities and other debt securities
Defined Benefit Plan Disclosure
Plan assets	$ 0	$ 0