Pension and Other Postemployment Benefits (Details 4) - OPEB - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 457	$ 410
Asset Allocation	100.00%	100.00%
Cash and short-term securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 72	$ 71
Asset Allocation	16.00%	17.00%
Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 246	$ 196
Asset Allocation	54.00%	48.00%
Government bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 100	$ 107
Asset Allocation	22.00%	26.00%
Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 34	$ 32
Asset Allocation	7.00%	8.00%
Mortgaged-backed securities (non-government)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 5	$ 4
Asset Allocation	1.00%	1.00%
Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 246	$ 196
Level 1 | Cash and short-term securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	246	196
Level 1 | Government bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | Mortgaged-backed securities (non-government)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value
Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	211	214
Level 2 | Cash and short-term securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	72	71
Level 2 | Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 2 | Government bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	100	107
Level 2 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	34	32
Level 2 | Mortgaged-backed securities (non-government)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	5	4
Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Cash and short-term securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Government bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Corporate debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Mortgaged-backed securities (non-government)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 0	$ 0