Retirement Benefits (Details 7) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	$ 28,397	$ 28,564
Cash & cash equivalents
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2,864	4,141
U.S. Equity Securities [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2,859	3,366
Alternative Investment, Net Asset Value	1,170	1,053
International equities
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2,712	2,454
Alternative Investment, Net Asset Value	4,017	4,315
U.S. Treasuries
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	1,527	1,282
U.S. Government Agency
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	322	345
Non-U.S. Government
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	206	135
Corporate debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	4,175	4,406
Asset backed
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	297	255
High yield debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	164	866
Bank loans
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	20	248
Other
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	68	20
Fixed Income Funds
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Net Asset Value	1,386	129
Hedge Funds
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Net Asset Value	351	166
OpportunisticFunds
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Net Asset Value	1,367	873
Private Equity Funds [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Net Asset Value	2,510	2,091
Real Estate Funds [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Net Asset Value	2,382	2,419
Level 1
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	5,865	5,888
Level 1 | Cash & cash equivalents
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	209	55
Level 1 | U.S. Equity Securities [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2,859	3,365
Level 1 | International equities
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2,711	2,453
Level 1 | U.S. Treasuries
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	26	0
Level 1 | Corporate debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	34	0
Level 1 | High yield debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	11	0
Level 1 | Other
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	15	15
Level 2
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	9,346	11,626
Level 2 | Cash & cash equivalents
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2,655	4,086
Level 2 | U.S. Treasuries
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	1,501	1,282
Level 2 | U.S. Government Agency
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	322	345
Level 2 | Non-U.S. Government
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	206	135
Level 2 | Corporate debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	4,141	4,406
Level 2 | Asset backed
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	297	255
Level 2 | High yield debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	153	866
Level 2 | Bank loans
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	20	248
Level 2 | Other
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	51	3
Level 3
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	3	4
Level 3 | U.S. Equity Securities [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets		1
Level 3 | International equities
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	1	1
Level 3 | Other
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2	2
Pension and Other Post-retirement benefit plans [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Derivative Asset	76	34
Derivative Liability	(52)	(19)
Derivatives, notional amount	$ 3,200	$ 3,300