Income Taxes - Schedule of Components of Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Deferred tax assets, depreciation	$ 25	$ 38
Deferred tax assets, employee benefits	887	836
Deferred tax assets, loss provisions	92	94
Deferred tax assets, deferred income	96	22
Deferred tax assets, interest	56	0
Deferred tax assets, tax loss carryforwards	2,932	3,159
Deferred tax assets, tax credit carryforwards	379	579
Deferred tax assets, other	52	94
Deferred tax assets, gross	4,519	4,822
Valuation allowance	(2,256)	(2,486)	$ (2,584)	$ (1,940)
Deferred tax assets, net	2,263	2,336
Deferred tax liabilities, depreciation	729	694
Deferred tax liabilities, employee benefits	16	27
Deferred tax liabilities, loss provisions	0	0
Deferred tax liabilities, deferred expense	943	1,102
Deferred tax liabilities, interest	0	0
Deferred tax liabilities, tax loss carryforwards	0	0
Deferred tax liabilities, tax credit carryforwards	0	0
Deferred tax liabilities, other	16	20
Deferred tax liabilities, gross	1,704	1,843
Deferred tax liabilities, valuation allowance	0	0
Deferred tax liabilities, net	$ 1,704	$ 1,843