Retirement Plans (Fair Values Pension Plan Assets By Asset Class) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 11,368	$ 10,312	$ 10,923
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	3,807	3,508
Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	3,146	4,083
Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	29	(59)	(10)
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	66
Corporate Bonds [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,177	1,018
Corporate Bonds [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Corporate Bonds [Member] | Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,177	1,018
Corporate Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Government Securities [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2,778	870
Government Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Government Securities [Member] | Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2,778	870
Government Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Mortgage Backed Securities [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1	41
Mortgage Backed Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Mortgage Backed Securities [Member] | Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	40
Mortgage Backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1	1	0
Other Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	232
Other Fixed Income [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	(802)	245
Other Fixed Income [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Other Fixed Income [Member] | Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	(814)	234
Other Fixed Income [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	12	11	10
Commodities [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	324
Commodities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Commodities [Member] | Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	324
Commodities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Derivatives [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		402
Derivatives [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	8	(71)
Derivatives [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Derivatives [Member] | Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	(8)	0
Derivatives [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	16	(71)	$ (20)
Cash and Cash Equivalents [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	397	322
Cash and Cash Equivalents [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	397	322
Cash and Cash Equivalents [Member] | Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Cash and Cash Equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	927	891
Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	481	472
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,106	1,015
Non-US [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	866
Non-US [Member] | Equity Securities [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2,132	2,575
Non-US [Member] | Equity Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2,119	1,806
Non-US [Member] | Equity Securities [Member] | Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	13	769
Non-US [Member] | Equity Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
United States (h) | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	708
United States (h) | Equity Securities [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,291	2,208
United States (h) | Equity Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,291	1,380
United States (h) | Equity Securities [Member] | Significant Observable Inputs (Level 2) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	828
United States (h) | Equity Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 0	$ 0