Retirement Benefits (Details 9) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	$ 28,564	$ 25,592
Derivatives, notional amount	89	147
Cash & cash equivalents
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	4,141	2,549
U.S. Equity Securities [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	3,366	3,689
Alternative Investment, Fair Value Disclosure	1,053	700
International equities
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2,454	2,441
Alternative Investment, Fair Value Disclosure	4,315	3,329
U.S. Treasuries
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	1,282	1,109
U.S. Government Agency
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	345	424
Corporate Bond [Domain]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2	0
Non-U.S. Government
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	135	108
Corporate debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	4,404	3,723
Asset backed
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	255	297
High yield debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	866	1,844
Bank loans
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	248	297
Other
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	20	2
Fixed Income Funds
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Fair Value Disclosure	129	99
Hedge Funds
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Fair Value Disclosure	166	220
OpportunisticFunds
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Fair Value Disclosure	873	581
Private Equity Funds [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Fair Value Disclosure	2,091	1,801
Real Estate [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Alternative Investment, Fair Value Disclosure	2,419	2,379
Level 1
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	5,888	6,140
Level 1 | Cash & cash equivalents
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	55	72
Level 1 | U.S. Equity Securities [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	3,365	3,686
Level 1 | International equities
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2,453	2,392
Level 1 | Other
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	15	(10)
Level 2
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	11,626	10,338
Level 2 | Cash & cash equivalents
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	4,086	2,477
Level 2 | International equities
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	0	48
Level 2 | U.S. Treasuries
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	1,282	1,109
Level 2 | U.S. Government Agency
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	345	424
Level 2 | Corporate Bond [Domain]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2	0
Level 2 | Non-U.S. Government
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	135	108
Level 2 | Corporate debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	4,404	3,723
Level 2 | Asset backed
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	255	296
Level 2 | High yield debt
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	866	1,844
Level 2 | Bank loans
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	248	297
Level 2 | Other
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	3	12
Level 3
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	4	5
Level 3 | U.S. Equity Securities [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	1	3
Level 3 | International equities
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	1	1
Level 3 | Asset backed
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	0	1
Level 3 | Other
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Fair value of plan assets	2	0
Pension and Other Post-retirement benefit plans [Member]
Plan Assets by Fair Value Measurement Input (Table Amounts) [Abstract]
Derivative Asset	34	19
Derivative Liability	(19)	(28)
Derivatives, notional amount	$ 3,300	$ 2,000