Pension and Other Postretirement Benefits (Fair Value Measurements) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 3,734	$ 4,224	$ 4,184
Postretirement benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4	5	5
Cash and cash equivalents [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	75	48
Fixed income securities [Member] | Postretirement benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4	5
Fixed income securities [Member] | US treasury securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	118	139
Fixed income securities [Member] | Government-related securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	295	350
Fixed income securities [Member] | Corporate bonds [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,208	2,560
Fixed income securities [Member] | Mortgage-backed and asset-backed securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	116	119
Equity securities [Member] | US large capitalization [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	555	607
Equity securities [Member] | US small capitalization [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	72	76
Equity securities [Member] | International equity [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	230	242
Limited partnerships [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	43	56
Other investments [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22	27
Level 1 [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	453	525
Level 1 [Member] | Cash and cash equivalents [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	5
Level 1 [Member] | Fixed income securities [Member] | US treasury securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	118	139
Level 1 [Member] | Fixed income securities [Member] | Government-related securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29	49
Level 1 [Member] | Fixed income securities [Member] | Corporate bonds [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Fixed income securities [Member] | Mortgage-backed and asset-backed securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Equity securities [Member] | US large capitalization [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	233	258
Level 1 [Member] | Equity securities [Member] | US small capitalization [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	70	74
Level 1 [Member] | Equity securities [Member] | International equity [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Limited partnerships [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Other investments [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,236	3,640
Level 2 [Member] | Cash and cash equivalents [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	72	43
Level 2 [Member] | Fixed income securities [Member] | US treasury securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Fixed income securities [Member] | Government-related securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	266	301
Level 2 [Member] | Fixed income securities [Member] | Corporate bonds [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,208	2,560
Level 2 [Member] | Fixed income securities [Member] | Mortgage-backed and asset-backed securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	114	116
Level 2 [Member] | Equity securities [Member] | US large capitalization [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	322	349
Level 2 [Member] | Equity securities [Member] | US small capitalization [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	2
Level 2 [Member] | Equity securities [Member] | International equity [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	230	242
Level 2 [Member] | Equity securities [Member] | International equity [Member] | Emerging Markets Investments [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	44	50
Level 2 [Member] | Limited partnerships [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Other investments [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22	27
Level 3 [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45	59	$ 59
Level 3 [Member] | Cash and cash equivalents [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Fixed income securities [Member] | US treasury securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Fixed income securities [Member] | Government-related securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Fixed income securities [Member] | Corporate bonds [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Fixed income securities [Member] | Mortgage-backed and asset-backed securities [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	3
Level 3 [Member] | Equity securities [Member] | US large capitalization [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Equity securities [Member] | US small capitalization [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Equity securities [Member] | International equity [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Limited partnerships [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	43	56
Level 3 [Member] | Other investments [Member] | Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0