Employee Benefit Plans - Narrative (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) plan	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate assumed next fiscal year	6.50%
Health care cost trend rate	4.50%
Multiemployer plan, contributions by employer	$ 0	$ 3,000,000	$ 158,000,000
Defined contribution plan, employer matching contribution per dollar	$ 1.00
Defined contribution plan, employer matching contribution	5.00%
Defined contribution plan, employers matching contribution for vesting plan	4.00%
Defined contribution plan, employers matching contribution for vesting, period	3 years
Defined contribution plans, cost	$ 236,000,000	235,000,000
Number of non-qualified defined contribution plans | plan	2
Defined contribution plan, assets and liabilities	$ 314,000,000	276,000,000
Fair value measured at Net Asset Value per share
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair values of the plan assets	$ 3,072,000,000	$ 2,988,000,000
Fair value measured at Net Asset Value per share | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of plan assets valued using NAV	21.00%	20.00%
Fair value measured at Net Asset Value per share | Fixed income and cash investment funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of plan assets valued using NAV	59.00%	62.00%
Fair value measured at Net Asset Value per share | Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of plan assets valued using NAV	20.00%	18.00%
Pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension assets or obligations, threshold, per plan	$ 20,000,000
Fair values of the plan assets	3,202,000,000	$ 3,004,000,000	1,866,000,000
Actual return on plan assets	347,000,000	314,000,000
Employer contributions	20,000,000	23,000,000
Pension plan | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated future employer contributions in next fiscal year	20,000,000
Pension plan | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated future employer contributions in next fiscal year	35,000,000
Pension plan | Fixed income and cash investment funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair values of the plan assets	1,807,000,000	1,858,000,000
Pension plan | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair values of the plan assets	130,000,000	16,000,000
Pension plan | Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair values of the plan assets	120,000,000	0
Plan assets level 3 reconciliation increase for purchase	124,000,000
Actual return on plan assets	4,000,000
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair values of the plan assets	0	0	$ 0
Actual return on plan assets	0	0
Employer contributions	19,000,000	$ 16,000,000
Estimated future employer contributions in next fiscal year	$ 10,000,000
U.S. | Pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of retirement plans | plan	4
Foreign | Pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of retirement plans | plan	7