Employee Benefit Plans - Fair Value of Plan Assets (Details) - Defined Benefit Plans - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	$ 813	$ 813	$ 906	$ 934	$ 813
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	813	906
Fair value of plan assets at end of year	$ 934	$ 813	$ 906
Expected long term rate of return on the pension assets (as a percent)	5.23%	5.23%	5.71%
Target allocation (as a percent)				100.00%
Allocation (as a percent)				100.00%	100.00%
Minimum
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Expected long term rate of return on the pension assets (as a percent)	5.71%
Maximum
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Expected long term rate of return on the pension assets (as a percent)	5.23%
Recurring basis
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	$ 813	$ 813		$ 934	$ 813
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	813
Fair value of plan assets at end of year	934	813
Recurring basis | Fair Value Amounts Using Quoted Prices in Active Markets for Identical Assets (Level 1)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	260	260		227	260
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	260
Fair value of plan assets at end of year	227	260
Recurring basis | Significant Other Observable Inputs (Level 2)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	518	518		674	518
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	518
Fair value of plan assets at end of year	674	518
Recurring basis | Significant Unobservable Inputs (Level 3)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	35	35		$ 33	$ 35
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	35
Fair value of plan assets at end of year	33	35
Equities
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Target allocation (as a percent)				20.00%
Allocation (as a percent)				19.00%	26.00%
Equities | Recurring basis
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	213	213		$ 196	$ 213
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	213
Fair value of plan assets at end of year	196	213
Equities | Recurring basis | Fair Value Amounts Using Quoted Prices in Active Markets for Identical Assets (Level 1)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	202	202		179	202
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	202
Fair value of plan assets at end of year	179	202
Equities | Recurring basis | Significant Other Observable Inputs (Level 2)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	11	11		17	11
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	11
Fair value of plan assets at end of year	17	11
Equities | Recurring basis | Significant Unobservable Inputs (Level 3)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	0	0		$ 0	$ 0
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Fixed income
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Target allocation (as a percent)				72.00%
Allocation (as a percent)				73.00%	64.00%
Fixed income | Recurring basis
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	547	547		$ 692	$ 547
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	547
Fair value of plan assets at end of year	692	547
Fixed income | Recurring basis | Fair Value Amounts Using Quoted Prices in Active Markets for Identical Assets (Level 1)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	39	39		42	39
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	39
Fair value of plan assets at end of year	42	39
Fixed income | Recurring basis | Significant Other Observable Inputs (Level 2)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	501	501		643	501
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	501
Fair value of plan assets at end of year	643	501
Fixed income | Recurring basis | Significant Unobservable Inputs (Level 3)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	7	7	$ 7	$ 7	$ 7
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	7	7
Return on pension plan assets	0	0
Purchases, sales and settlements	0	0
Transfers (out of) into Level 3	0	0
Fair value of plan assets at end of year	7	7	7
Real estate/other
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Target allocation (as a percent)				1.00%
Allocation (as a percent)				1.00%	1.00%
Real estate/other | Recurring basis
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	34	34		$ 40	$ 34
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	34
Fair value of plan assets at end of year	40	34
Real estate/other | Recurring basis | Fair Value Amounts Using Quoted Prices in Active Markets for Identical Assets (Level 1)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	0	0		0	0
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Real estate/other | Recurring basis | Significant Other Observable Inputs (Level 2)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	6	6		14	6
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	6
Fair value of plan assets at end of year	14	6
Real estate/other | Recurring basis | Significant Unobservable Inputs (Level 3)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	26	30	30	26	28
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	28	30
Return on pension plan assets	(1)	(1)
Purchases, sales and settlements	(1)	(1)
Transfers (out of) into Level 3	0	0
Disposals	0	0
Fair value of plan assets at end of year	26	28	$ 30
Cash and cash equivalents | Recurring basis
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	19	19		6	19
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	19
Fair value of plan assets at end of year	6	19
Cash and cash equivalents | Recurring basis | Fair Value Amounts Using Quoted Prices in Active Markets for Identical Assets (Level 1)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	19	19		6	19
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	19
Fair value of plan assets at end of year	6	19
Cash and cash equivalents | Recurring basis | Significant Other Observable Inputs (Level 2)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	0	0		0	0
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Cash and cash equivalents | Recurring basis | Significant Unobservable Inputs (Level 3)
EMPLOYEE BENEFIT PLANS
Fair value of plan assets	0	0		$ 0	$ 0
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	$ 0	$ 0
Cash
Fair Value Measurements of Plan Assets Using Significant Unobservable Inputs (Level 3)
Target allocation (as a percent)				7.00%
Allocation (as a percent)				7.00%	9.00%