Pension Plans and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer contributions	$ 550	$ 334	$ 314
Pre-tax settlement losses	0	0	(187)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-tax settlement losses	0	0	(187)
Employer contributions	25	12	46
Multiemployer plans, plan contributions	18	18	17
Benefit obligation	6,239	5,841	131
Net periodic benefit cost	$ (131)	(6)	208
Pension Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	33.00%
Pension Plan | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	54.00%
Pension Plan | Real Estate Investment
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	6.00%
Pension Plan | Private equity investments
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	4.00%
Pension Plan | Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	3.00%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Multiemployer plans, plan contributions	$ 57	58	58
Benefit obligation	246	228
Net periodic benefit cost	$ 7	$ 2	$ 1