Pension and Other Postretirement Benefits, Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plans [Member]
Equity securities [Abstract]
Fair value of company's plan assets	$ 2,840	$ 3,047	$ 2,721
Pension Plans [Member] | U.S. [Member]
Equity securities [Abstract]
Liabilities for unsettled trades, net	(9)	(30)
Fair value of company's plan assets	$ 2,537	$ 2,704
Percentage of mutual fund in total investment in fixed income - investment grade securities	66.00%	62.00%
Percentage of pooled bond funds in total investment in fixed income - investment grade securities	34.00%	38.00%
Pension Plans [Member] | U.S. [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	$ 1,793	$ 1,909
Pension Plans [Member] | U.S. [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	577	622
Pension Plans [Member] | U.S. [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | U.S. Equity [Member]
Equity securities [Abstract]
Fair value of company's plan assets	1,205	1,297
Pension Plans [Member] | U.S. [Member] | U.S. Equity [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	1,205	1,297
Pension Plans [Member] | U.S. [Member] | U.S. Equity [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | U.S. Equity [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | International Equity [Member]
Equity securities [Abstract]
Fair value of company's plan assets	90	87
Pension Plans [Member] | U.S. [Member] | International Equity [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	90	87
Pension Plans [Member] | U.S. [Member] | International Equity [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | International Equity [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | Fixed Income - Investment Grade [Member]
Equity securities [Abstract]
Fair value of company's plan assets	473	534
Pension Plans [Member] | U.S. [Member] | Fixed Income - Investment Grade [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	313	329
Pension Plans [Member] | U.S. [Member] | Fixed Income - Investment Grade [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	160	205
Pension Plans [Member] | U.S. [Member] | Fixed Income - Investment Grade [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | Fixed Income - High Yield [Member]
Equity securities [Abstract]
Fair value of company's plan assets	271	219
Pension Plans [Member] | U.S. [Member] | Fixed Income - High Yield [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | Fixed Income - High Yield [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	271	219
Pension Plans [Member] | U.S. [Member] | Fixed Income - High Yield [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | Real Estate Investment Trusts [Member]
Equity securities [Abstract]
Fair value of company's plan assets	185	196
Pension Plans [Member] | U.S. [Member] | Real Estate Investment Trusts [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	185	196
Pension Plans [Member] | U.S. [Member] | Real Estate Investment Trusts [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | Real Estate Investment Trusts [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | Other [Member]
Equity securities [Abstract]
Fair value of company's plan assets	146	198
Pension Plans [Member] | U.S. [Member] | Other [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | Other [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	146	198
Pension Plans [Member] | U.S. [Member] | Other [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | U.S. [Member] | Total Assets at Fair Value [Member]
Equity securities [Abstract]
Fair value of company's plan assets	2,370	2,531
Pension Plans [Member] | U.S. [Member] | Other Investments Measured at Net Asset Value [Member]
Equity securities [Abstract]
Fair value of company's plan assets	176	203
Pension Plans [Member] | Canada [Member]
Equity securities [Abstract]
Liabilities for unsettled trades, net	0	0
Fair value of company's plan assets	$ 303	$ 343
Percentage of mutual fund investment in equity trust funds	30.00%	31.00%
Percentage of pooled bond fund investment in equity trust funds	70.00%	69.00%
Pension Plans [Member] | Canada [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	$ 163	$ 184
Pension Plans [Member] | Canada [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	16	37
Pension Plans [Member] | Canada [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | U.S. Equity [Member]
Equity securities [Abstract]
Fair value of company's plan assets	64	71
Pension Plans [Member] | Canada [Member] | U.S. Equity [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	64	71
Pension Plans [Member] | Canada [Member] | U.S. Equity [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | U.S. Equity [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | International Equity [Member]
Equity securities [Abstract]
Fair value of company's plan assets	95	105
Pension Plans [Member] | Canada [Member] | International Equity [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	95	105
Pension Plans [Member] | Canada [Member] | International Equity [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | International Equity [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Fixed Income - Investment Grade [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Fixed Income - Investment Grade [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Fixed Income - Investment Grade [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Fixed Income - Investment Grade [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Fixed Income - High Yield [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Fixed Income - High Yield [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Fixed Income - High Yield [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Fixed Income - High Yield [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Real Estate Investment Trusts [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Real Estate Investment Trusts [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Real Estate Investment Trusts [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Real Estate Investment Trusts [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Other [Member]
Equity securities [Abstract]
Fair value of company's plan assets	20	45
Pension Plans [Member] | Canada [Member] | Other [Member] | Level 1 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	4	8
Pension Plans [Member] | Canada [Member] | Other [Member] | Level 2 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	16	37
Pension Plans [Member] | Canada [Member] | Other [Member] | Level 3 [Member]
Equity securities [Abstract]
Fair value of company's plan assets	0	0
Pension Plans [Member] | Canada [Member] | Total Assets at Fair Value [Member]
Equity securities [Abstract]
Fair value of company's plan assets	179	221
Pension Plans [Member] | Canada [Member] | Other Investments Measured at Net Asset Value [Member]
Equity securities [Abstract]
Fair value of company's plan assets	$ 124	$ 122
Minimum [Member]
Equity securities [Abstract]
Notice Required Prior to Withdrawal from Bond Funds	0 days
Maximum [Member]
Equity securities [Abstract]
Notice Required Prior to Withdrawal from Bond Funds	3 days