Fair Value Measurements (U.S. Pension Benefit Plans) (Details) - U.S. Pension Benefit Plans - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Cash	$ 5
Accrued income receivable		$ 9
Fair value plan assets	3,195	3,130	$ 3,317
Total Investment securities
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	3,190	3,121
Common stock and equivalents
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	95	89
Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	1,589	1,541
Preferred stock
Defined Benefit Plan Disclosure [Line Items]
Total investments securities		2
Government, agency and government-sponsored enterprise obligations
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	125	120
Other government bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	54	70
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	823	862
Mortgage-backed bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	2	2
Commingled bond funds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	319
Commingled short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	183	435
Level 1 | Total Investment securities
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	1,635	91
Level 1 | Common stock and equivalents
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	95	89
Level 1 | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	1,096	0
Level 1 | Preferred stock
Defined Benefit Plan Disclosure [Line Items]
Total investments securities		2
Level 1 | Government, agency and government-sponsored enterprise obligations
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	0	0
Level 1 | Other government bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	0	0
Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	0	0
Level 1 | Mortgage-backed bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	0	0
Level 1 | Commingled bond funds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	261
Level 1 | Commingled short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	183	0
Level 2 | Total Investment securities
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	1,555	3,030
Level 2 | Common stock and equivalents
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	0	0
Level 2 | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	493	1,541
Level 2 | Preferred stock
Defined Benefit Plan Disclosure [Line Items]
Total investments securities		0
Level 2 | Government, agency and government-sponsored enterprise obligations
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	125	120
Level 2 | Other government bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	54	70
Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	823	862
Level 2 | Mortgage-backed bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	2	2
Level 2 | Commingled bond funds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	58
Level 2 | Commingled short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total investments securities	$ 0	$ 435