Retirement Benefits - Fair Value Recurring Basis (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Cash equivalents	$ 1,230,000,000	[1]	$ 995,000,000	[1]
Fixed income [Abstract]
Total pension and other postretirement benefit plan assets	15,766,000,000	[2]	15,411,000,000
Fair Value Defined Benefit Plan Measured On Recurring Basis Financial Statement Footnotes [Abstract]
Derivative, Notional Amount	2,651,000,000		2,498,000,000
Net Assets Pending Transactions Excluded	43,000,000		81,000,000
Pension Plans Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash equivalents			1,000,000
Equity Securities [Abstract]
Individually held	3,092,000,000		2,562,000,000
Commingled funds	1,167,000,000		1,111,000,000
Mutual funds	270,000,000		323,000,000
Equity securities subtotal	4,529,000,000		3,996,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	917,000,000		1,037,000,000
Debt securities issued by states of the United States and political subdivisions of the states	88,000,000		108,000,000
Foreign debt	205,000,000		252,000,000
Corporate debt securities	2,968,000,000		3,330,000,000
Federal agency mortgage-backed securities	90,000,000		117,000,000
Non-federal agency mortgage-backed securities	26,000,000		28,000,000
Commingled funds fixed income	558,000,000		274,000,000
Mutual funds fixed income	320,000,000		295,000,000
Fixed income subtotal	5,045,000,000		5,429,000,000	[2]
Hedge funds	2,305,000,000		2,315,000,000
Private equity	806,000,000		754,000,000
Real estate	848,000,000		781,000,000
Pension plan assets	13,533,000,000		13,276,000,000
Pension Plans Defined Benefit [Member] | Individually Held [Member]
Fixed income [Abstract]
Real estate	264,000,000		280,000,000
Pension Plans Defined Benefit [Member] | Commingled Funds [Member]
Fixed income [Abstract]
Real estate	2,000,000		75,000,000
Pension Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	582,000,000		426,000,000
Pension Plans Defined Benefit [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Derivative Instruments	7,000,000	[3]	9,000,000	[3]
Pension Plans Defined Benefit [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Derivative Instruments	(134,000,000)	[3]
Hedge funds			(21,000,000)	[3]
Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash equivalents	51,000,000		44,000,000
Equity Securities [Abstract]
Individually held	286,000,000		198,000,000
Commingled funds	515,000,000		530,000,000
Mutual funds	164,000,000		230,000,000
Equity securities subtotal	965,000,000		958,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	18,000,000		18,000,000
Debt securities issued by states of the United States and political subdivisions of the states	149,000,000		125,000,000
Foreign debt	2,000,000		3,000,000
Corporate debt securities	50,000,000		50,000,000
Federal agency mortgage-backed securities	45,000,000		52,000,000
Non-federal agency mortgage-backed securities	7,000,000		6,000,000
Commingled funds fixed income	218,000,000		271,000,000
Mutual funds fixed income	305,000,000		297,000,000
Fixed income subtotal	794,000,000		822,000,000
Hedge funds	299,000,000		200,000,000
Private equity	2,000,000		1,000,000
Real estate	122,000,000		110,000,000
Postretirement benefit plan subtotal	2,233,000,000		2,135,000,000
Other Postretirement Benefit Plans Defined Benefit [Member] | Individually Held [Member]
Fixed income [Abstract]
Real estate	8,000,000		7,000,000
Other Postretirement Benefit Plans Defined Benefit [Member] | Commingled Funds [Member]
Fixed income [Abstract]
Real estate			2,000,000
Other Postretirement Benefit Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	114,000,000		101,000,000
Fair Value Inputs Level 1 [Member]
Fixed income [Abstract]
Total pension and other postretirement benefit plan assets	5,368,000,000	[2]	4,999,000,000
Fair Value Inputs Level 1 [Member] | Pension Plans Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash equivalents			1,000,000
Equity Securities [Abstract]
Individually held	3,090,000,000		2,562,000,000
Mutual funds	270,000,000		323,000,000
Equity securities subtotal	3,360,000,000		2,885,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	908,000,000		1,037,000,000
Mutual funds fixed income	5,000,000		4,000,000
Fixed income subtotal	913,000,000		1,041,000,000	[2]
Real estate	264,000,000		280,000,000
Pension plan assets	4,537,000,000		4,207,000,000
Fair Value Inputs Level 1 [Member] | Pension Plans Defined Benefit [Member] | Individually Held [Member]
Fixed income [Abstract]
Hedge funds			280,000,000
Real estate	264,000,000
Fair Value Inputs Level 1 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash equivalents	51,000,000		44,000,000
Equity Securities [Abstract]
Individually held	286,000,000		198,000,000
Mutual funds	164,000,000		230,000,000
Equity securities subtotal	450,000,000		428,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	17,000,000		18,000,000
Mutual funds fixed income	305,000,000		295,000,000
Fixed income subtotal	322,000,000		313,000,000
Real estate	8,000,000		7,000,000
Postretirement benefit plan subtotal	831,000,000		792,000,000
Fair Value Inputs Level 1 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member] | Individually Held [Member]
Fixed income [Abstract]
Real estate	8,000,000		7,000,000
Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Total pension and other postretirement benefit plan assets	7,813,000,000	[2]	7,889,000,000
Fair Value Inputs Level 2 [Member] | Pension Plans Defined Benefit [Member]
Equity Securities [Abstract]
Commingled funds	1,167,000,000		1,111,000,000
Mutual funds			0
Equity securities subtotal	1,167,000,000		1,111,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	9,000,000
Debt securities issued by states of the United States and political subdivisions of the states	88,000,000		108,000,000
Foreign debt	205,000,000		252,000,000
Corporate debt securities	2,927,000,000		3,330,000,000
Federal agency mortgage-backed securities	90,000,000		117,000,000
Non-federal agency mortgage-backed securities	26,000,000		28,000,000
Commingled funds fixed income	558,000,000		274,000,000
Mutual funds fixed income	315,000,000		291,000,000
Fixed income subtotal	4,091,000,000		4,388,000,000	[2]
Hedge funds	1,266,000,000		1,080,000,000
Real estate	2,000,000		75,000,000
Pension plan assets	6,526,000,000		6,654,000,000
Fair Value Inputs Level 2 [Member] | Pension Plans Defined Benefit [Member] | Commingled Funds [Member]
Fixed income [Abstract]
Real estate	2,000,000		75,000,000
Fair Value Inputs Level 2 [Member] | Pension Plans Defined Benefit [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Derivative Instruments	7,000,000	[3]	9,000,000	[3]
Fair Value Inputs Level 2 [Member] | Pension Plans Defined Benefit [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Derivative Instruments	(134,000,000)	[3]	(21,000,000)	[3]
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member]
Equity Securities [Abstract]
Commingled funds	515,000,000		530,000,000
Equity securities subtotal	515,000,000		530,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,000,000
Debt securities issued by states of the United States and political subdivisions of the states	149,000,000		125,000,000
Foreign debt	2,000,000		3,000,000
Corporate debt securities	50,000,000		50,000,000
Federal agency mortgage-backed securities	45,000,000		52,000,000
Non-federal agency mortgage-backed securities	7,000,000		6,000,000
Commingled funds fixed income	218,000,000		271,000,000
Mutual funds fixed income			2,000,000
Fixed income subtotal	472,000,000		509,000,000
Hedge funds	295,000,000		188,000,000
Real estate	5,000,000		8,000,000
Postretirement benefit plan subtotal	1,287,000,000		1,235,000,000
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member] | Commingled Funds [Member]
Fixed income [Abstract]
Real estate			2,000,000
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	5,000,000		6,000,000
Fair Value Inputs Level 3 [Member]
Fixed income [Abstract]
Total pension and other postretirement benefit plan assets	2,585,000,000	[2]	2,523,000,000
Fair Value Inputs Level 3 [Member] | Pension Plans Defined Benefit [Member]
Equity Securities [Abstract]
Individually held	2,000,000
Equity securities subtotal	2,000,000
Fixed income [Abstract]
Corporate debt securities	41,000,000
Fixed income subtotal	41,000,000
Hedge funds	1,039,000,000		1,235,000,000
Private equity	806,000,000		754,000,000
Real estate	582,000,000		426,000,000
Pension plan assets	2,470,000,000		2,415,000,000
Fair Value Inputs Level 3 [Member] | Pension Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	582,000,000		426,000,000
Fair Value Inputs Level 3 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member]
Fixed income [Abstract]
Hedge funds	4,000,000		12,000,000
Private equity	2,000,000		1,000,000
Real estate	109,000,000		95,000,000
Postretirement benefit plan subtotal	115,000,000		108,000,000
Fair Value Inputs Level 3 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	$ 109,000,000		$ 95,000,000

[1] Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value.

[2] Excludes net assets of $43 million and $81 million at December 31, 2013 and 2012, respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables related to pending securities sales, interest and dividends receivable, and payables related to pending securities purchases.

[3] Derivative instruments have a total notional amount of $2,651 million and $2,498 million at December 31, 2013 and 2012, respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company’s exposure to credit or market loss.