Accumulated Other Comprehensive Income Reclassifications out of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Balance	$ 130	$ 231	$ 119
Other comprehensive income (loss), net before reclassifications	15	(125)	114
Tax expense (benefit)	(1)	1	0
Balance	145	130	231
Amortization of net gain
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax		1
Amortization of prior service credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	(4)	(3)	(2)
Settlement lossa
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	5
Reclassification due to ASU 2016-01 adoption
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax		1
Reclassification due to ASU 2018-02 adoption
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax		(26)
Equity Method Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Balance	(3)	(3)	(3)
Other comprehensive income (loss), net before reclassifications	(1)	1	0
Tax expense (benefit)	0	0	0
Balance	(4)	(3)	(3)
Equity Method Investments | Amortization of net gain
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax		0
Equity Method Investments | Amortization of prior service credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	0	0	0
Equity Method Investments | Settlement lossa
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	0
Equity Method Investments | Reclassification due to ASU 2016-01 adoption
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax		1
Equity Method Investments | Reclassification due to ASU 2018-02 adoption
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax		0
Pension and Retiree Health and Welfare Benefit Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Balance	133	234	122
Other comprehensive income (loss), net before reclassifications	16	(126)	114
Tax expense (benefit)	(1)	1	0
Balance	149	133	234
Pension and Retiree Health and Welfare Benefit Items | Amortization of net gain
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax		1
Pension and Retiree Health and Welfare Benefit Items | Amortization of prior service credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	(4)	(3)	$ (2)
Pension and Retiree Health and Welfare Benefit Items | Settlement lossa
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before Tax	$ 5
Pension and Retiree Health and Welfare Benefit Items | Reclassification due to ASU 2016-01 adoption
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax		0
Pension and Retiree Health and Welfare Benefit Items | Reclassification due to ASU 2018-02 adoption
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax		$ (26)