Fair Value Measurements (U.S. Plans) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	$ 3,317	$ 6,071	$ 5,426
Level 1
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	20	38
Level 1 | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	905	1,430
Level 1 | Common stock and equivalents
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	20	38
Level 1 | Common stock and equivalents | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	902	1,424
Level 1 | Commingled equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Commingled equity funds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	0	0
Level 1 | Preferred stock | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	3	6
Level 1 | Government, agency and government-sponsored enterprise obligations
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Government, agency and government-sponsored enterprise obligations | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	0	0
Level 1 | Other government bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Other government bonds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	0	0
Level 1 | Corporate bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Corporate bonds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	0	0
Level 1 | Mortgage-backed bonds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	0	0
Level 1 | Commingled bond funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Commingled bond funds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities		0
Level 1 | Commingled short-term investment funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Commingled short-term investment funds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	0	0
Level 2
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	143	123
Level 2 | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	2,409	4,634
Level 2 | Common stock and equivalents
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 2 | Common stock and equivalents | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	0	0
Level 2 | Commingled equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	13	55
Level 2 | Commingled equity funds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	565	2,045
Level 2 | Preferred stock | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	0	0
Level 2 | Government, agency and government-sponsored enterprise obligations
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	11	6
Level 2 | Government, agency and government-sponsored enterprise obligations | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	520	238
Level 2 | Other government bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	2	1
Level 2 | Other government bonds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	91	42
Level 2 | Corporate bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	18	9
Level 2 | Corporate bonds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	795	336
Level 2 | Mortgage-backed bonds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	16	15
Level 2 | Commingled bond funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	49
Level 2 | Commingled bond funds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities		1,862
Level 2 | Commingled short-term investment funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	99	3
Level 2 | Commingled short-term investment funds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	422	96
Total
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	163	161
Total | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	3,314	6,064
Accrued income receivable	3	7
Fair value plan assets	3,317	6,071
Total | Common stock and equivalents
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	20	38
Total | Common stock and equivalents | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	902	1,424
Total | Commingled equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	13	55
Total | Commingled equity funds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	565	2,045
Total | Preferred stock | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	3	6
Total | Government, agency and government-sponsored enterprise obligations
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	11	6
Total | Government, agency and government-sponsored enterprise obligations | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	520	238
Total | Other government bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	2	1
Total | Other government bonds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	91	42
Total | Corporate bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	18	9
Total | Corporate bonds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	795	336
Total | Mortgage-backed bonds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	16	15
Total | Commingled bond funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	49
Total | Commingled bond funds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities		1,862
Total | Commingled short-term investment funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	99	3
Total | Commingled short-term investment funds | U.S. Pension Benefit Plans
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total marketable securities	$ 422	$ 96