Retirement Benefits - Fair Value Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Fair Value Defined Benefit Plan Measured On Recurring Basis Financial Statement Captions [Line Items]
Cash equivalents	$ 995.00	[1]	$ 861.00	[1]
Equity Securities [Abstract]
Individually held			1,985.00
Mutual funds	4.00
Fixed income [Abstract]
Real estate			125.00
Total pension and other postretirement benefit plan assets	15,411.00		12,986.00
Pension Plans Defined Benefit [Member]
Fair Value Defined Benefit Plan Measured On Recurring Basis Financial Statement Captions [Line Items]
Cash equivalents	1.00		8.00
Equity Securities [Abstract]
Individually held	2,562.00
Commingled funds	1,111.00		858.00
Mutual funds	323.00		389.00
Equity securities subtotal	3,996.00		3,232.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,037.00		1,664.00
Debt securities issued by states of the United States and political subdivisions of the states	108.00		88.00
Foreign debt	252.00		224.00
Corporate debt securities	3,330.00		2,561.00
Federal agency mortgage-backed securities	117.00		156.00
Non-federal agency mortgage-backed securities	28.00		28.00
Commingled funds fixed income	274.00		202.00
Mutual funds fixed income	295.00		277.00
Fixed income subtotal	5,429.00		5,200.00
Hedge funds	2,315.00		1,525.00
Private equity	754.00		672.00
Real estate
Pension plan assets subtotal	13,276.00		11,198.00
Pension Plans Defined Benefit [Member] | Individually Held [Member]
Fixed income [Abstract]
Real estate	280.00		207.00
Pension Plans Defined Benefit [Member] | Commingled Funds [Member]
Fixed income [Abstract]
Real estate	75.00		125.00
Pension Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	426.00		229.00
Pension Plans Defined Benefit [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Derivative Instruments	9.00
Pension Plans Defined Benefit [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Derivative Instruments	(21.00)
Other Postretirement Benefit Plans Defined Benefit [Member]
Fair Value Defined Benefit Plan Measured On Recurring Basis Financial Statement Captions [Line Items]
Cash equivalents	44.00		73.00
Equity Securities [Abstract]
Individually held	198.00		110.00
Commingled funds	530.00		415.00
Mutual funds	230.00		171.00
Equity securities subtotal	958.00		696.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	18.00		29.00
Debt securities issued by states of the United States and political subdivisions of the states	125.00		93.00
Foreign debt	3.00		4.00
Corporate debt securities	50.00		41.00
Federal agency mortgage-backed securities	52.00		34.00
Non-federal agency mortgage-backed securities	6.00		7.00
Commingled funds fixed income	271.00		385.00
Mutual funds fixed income	297.00		256.00
Fixed income subtotal	822.00		849.00
Hedge funds	200.00		157.00
Private equity	1.00
Real estate
Postretirement benefit plan subtotal	2,135.00		1,788.00
Other Postretirement Benefit Plans Defined Benefit [Member] | Individually Held [Member]
Fixed income [Abstract]
Real estate	7.00		4.00
Other Postretirement Benefit Plans Defined Benefit [Member] | Commingled Funds [Member]
Fixed income [Abstract]
Real estate	2.00		1.00
Other Postretirement Benefit Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	101.00		7.00
Fair Value Inputs Level 1 [Member]
Fixed income [Abstract]
Total pension and other postretirement benefit plan assets	4,999.00		4,029.00
Fair Value Inputs Level 1 [Member] | Pension Plans Defined Benefit [Member]
Fair Value Defined Benefit Plan Measured On Recurring Basis Financial Statement Captions [Line Items]
Cash equivalents	1.00		8.00
Equity Securities [Abstract]
Individually held	2,562.00		1,985.00
Mutual funds	323.00
Equity securities subtotal	2,885.00		1,985.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,037.00		1,616.00
Fixed income subtotal	1,041.00		1,616.00
Real estate
Pension plan assets subtotal	4,207.00		3,816.00
Fair Value Inputs Level 1 [Member] | Pension Plans Defined Benefit [Member] | Individually Held [Member]
Fixed income [Abstract]
Real estate	280.00		207.00
Fair Value Inputs Level 1 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member]
Fair Value Defined Benefit Plan Measured On Recurring Basis Financial Statement Captions [Line Items]
Cash equivalents	44.00		73.00
Equity Securities [Abstract]
Individually held	198.00		110.00
Mutual funds	230.00
Equity securities subtotal	428.00		110.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	18.00		26.00
Mutual funds fixed income	295.00
Fixed income subtotal	313.00		26.00
Real estate
Postretirement benefit plan subtotal	792.00		213.00
Fair Value Inputs Level 1 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member] | Individually Held [Member]
Fixed income [Abstract]
Real estate	7.00		4.00
Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Total pension and other postretirement benefit plan assets	7,889.00		6,366.00
Fair Value Inputs Level 2 [Member] | Pension Plans Defined Benefit [Member]
Equity Securities [Abstract]
Commingled funds	1,111.00		858.00
Mutual funds	0		389.00
Equity securities subtotal	1,111.00		1,247.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0		48.00
Debt securities issued by states of the United States and political subdivisions of the states	108.00		88.00
Foreign debt	252.00		224.00
Corporate debt securities	3,330.00		2,561.00
Federal agency mortgage-backed securities	117.00		156.00
Non-federal agency mortgage-backed securities	28.00		28.00
Commingled funds fixed income	274.00		202.00
Mutual funds fixed income	291.00		277.00
Fixed income subtotal	4,388.00		3,584.00
Hedge funds	1,080.00		0
Real estate
Pension plan assets subtotal	6,654.00		4,956.00
Fair Value Inputs Level 2 [Member] | Pension Plans Defined Benefit [Member] | Commingled Funds [Member]
Fixed income [Abstract]
Real estate	75.00
Fair Value Inputs Level 2 [Member] | Pension Plans Defined Benefit [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Derivative Instruments	9.00
Fair Value Inputs Level 2 [Member] | Pension Plans Defined Benefit [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Derivative Instruments	(21.00)
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member]
Equity Securities [Abstract]
Commingled funds	530.00		415.00
Mutual funds	0		171.00
Equity securities subtotal	530.00		586.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0		3.00
Debt securities issued by states of the United States and political subdivisions of the states	125.00		93.00
Foreign debt	3.00		4.00
Corporate debt securities	50.00		41.00
Federal agency mortgage-backed securities	52.00		34.00
Non-federal agency mortgage-backed securities	6.00		7.00
Commingled funds fixed income	271.00		385.00
Mutual funds fixed income	2.00		256.00
Fixed income subtotal	509.00		823.00
Hedge funds	188.00		0
Real estate
Postretirement benefit plan subtotal	1,235.00		1,410.00
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member] | Commingled Funds [Member]
Fixed income [Abstract]
Real estate	2.00		1.00
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	6.00
Fair Value Inputs Level 3 [Member]
Fixed income [Abstract]
Hedge funds			1,525.00
Total pension and other postretirement benefit plan assets	2,523.00		2,591.00
Fair Value Inputs Level 3 [Member] | Pension Plans Defined Benefit [Member]
Fixed income [Abstract]
Hedge funds	1,235.00
Private equity	754.00		672.00
Real estate
Pension plan assets subtotal	2,415.00		2,426.00
Fair Value Inputs Level 3 [Member] | Pension Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	426.00		229.00
Fair Value Inputs Level 3 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member]
Fixed income [Abstract]
Fixed income subtotal	0
Hedge funds	12.00		157.00
Private equity	1.00
Real estate
Postretirement benefit plan subtotal	108.00		165.00
Fair Value Inputs Level 3 [Member] | Other Postretirement Benefit Plans Defined Benefit [Member] | Real Estate Funds [Member]
Fixed income [Abstract]
Real estate	$ 95.00		$ 7.00

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