Employee Retirement Plans (Domestic Defined Benefit Plan Assets) (Details) - Pension Benefits [Member] - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Fair value of plan assets		$ 3,539		$ 3,225		$ 3,058
Domestic [Member]
Fair value of plan assets		3,004		2,765		2,616
Domestic [Member] | Quoted Market Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of plan assets		392		412
Domestic [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair value of plan assets		2,360		2,066
Domestic [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair value of plan assets		252		287
Domestic [Member] | Equity Securities [Member] | U.S. Companies [Member]
Fair value of plan assets		374		318
Domestic [Member] | Equity Securities [Member] | U.S. Companies [Member] | Quoted Market Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of plan assets		57		47
Domestic [Member] | Equity Securities [Member] | U.S. Companies [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair value of plan assets		317		271
Domestic [Member] | Equity Securities [Member] | International Companies [Member]
Fair value of plan assets		420		340
Domestic [Member] | Equity Securities [Member] | International Companies [Member] | Quoted Market Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of plan assets		117		90
Domestic [Member] | Equity Securities [Member] | International Companies [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair value of plan assets		303		250
Domestic [Member] | Fixed Income Securities [Member] | U.S. Companies [Member]
Fair value of plan assets		1,815		1,608
Domestic [Member] | Fixed Income Securities [Member] | U.S. Companies [Member] | Quoted Market Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of plan assets		197		175
Domestic [Member] | Fixed Income Securities [Member] | U.S. Companies [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair value of plan assets		1,618		1,433
Domestic [Member] | Private Equity Funds [Member]
Fair value of plan assets	[1]	105		137
Domestic [Member] | Private Equity Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair value of plan assets		105	[1]	137	[1]	163
Domestic [Member] | Real Estate [Member]
Fair value of plan assets	[2]	147		150
Domestic [Member] | Real Estate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair value of plan assets		147	[2]	150	[2]	$ 61
Domestic [Member] | Cash Equivalents [Member]
Fair value of plan assets		21		100
Domestic [Member] | Cash Equivalents [Member] | Quoted Market Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of plan assets		21		100
Domestic [Member] | Commodity Option [Member]
Fair value of plan assets	[3]	122		112
Domestic [Member] | Commodity Option [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair value of plan assets	[3]	$ 122		$ 112

[1] This category includes venture capital, leverage buyouts and distressed debt limited partnerships invested primarily in U.S. companies. The inputs are valued by discounted cash flow analysis and comparable sale analysis.

[2] This category includes industrial, office, apartments, hotels, infrastructure and retail investments which are limited partnerships predominately in the U.S. The inputs are valued by discounted cash flow analysis; comparable sale analysis and periodic external appraisals.

[3] This category includes investments in energy, industrial metals, precious metals, agricultural and livestock primarily through futures, options, swaps and exchange traded funds.