Leases - Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Jan. 01, 2019
Maturities of operating lease liabilities
2021	$ 121
2022	92
2023	58
2024	47
2025	41
Thereafter	117
Total undiscounted lease payments	476
Less imputed interest	(47)
Total operating lease liability	429	$ 498
Maturities of finance lease liabilities
2021	14
2022	14
2023	14
2024	13
2025	12
Thereafter	45
Total undiscounted lease payments	112
Less imputed interest	(24)
Total finance lease liability	$ 88
Weighted average discount rate for operating leases	6.44%
Weighted average discount rate for financing leases	5.18%