Employee Postretirement Benefits (Pension Plan Assets of the Principal Plans Measured at fair value) (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	$ 203,000,000	$ 362,000,000
Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	4,860,000,000	4,478,000,000
Cash and Cash Equivalents - Assets Held Directly [Member]
Fair value of plan assets	23,000,000	24,000,000
Cash and Cash Equivalents - Assets Held Directly [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	23,000,000	24,000,000
Cash and Cash Equivalents - Assets Held Directly [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	0	0
Cash and Cash Equivalents - Held Through Mutual and Pooled Funds [Member]
Fair value of plan assets	143,000,000	180,000,000
Cash and Cash Equivalents - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	0	50,000,000
Cash and Cash Equivalents - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	143,000,000	130,000,000
U.S. Government and Municipals [Member] | Fixed Income - Assets Held Directly [Member]
Fair value of plan assets	132,000,000	187,000,000
U.S. Government and Municipals [Member] | Fixed Income - Assets Held Directly [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	31,000,000	93,000,000
U.S. Government and Municipals [Member] | Fixed Income - Assets Held Directly [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	101,000,000	94,000,000
U.S. Government and Municipals [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member]
Fair value of plan assets	490,000,000	472,000,000
U.S. Government and Municipals [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	0	0
U.S. Government and Municipals [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	490,000,000	472,000,000
U.S. Securitized Fixed Income [Member] | Fixed Income - Assets Held Directly [Member]
Fair value of plan assets	3,000,000	13,000,000
U.S. Securitized Fixed Income [Member] | Fixed Income - Assets Held Directly [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	0	0
U.S. Securitized Fixed Income [Member] | Fixed Income - Assets Held Directly [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	3,000,000	13,000,000
U.S. Corporate Debt [Member] | Fixed Income - Assets Held Directly [Member]
Fair value of plan assets	1,112,000,000	993,000,000
U.S. Corporate Debt [Member] | Fixed Income - Assets Held Directly [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	0	0
U.S. Corporate Debt [Member] | Fixed Income - Assets Held Directly [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	1,112,000,000	993,000,000
U.S. Corporate Debt [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member]
Fair value of plan assets	199,000,000	185,000,000
U.S. Corporate Debt [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	0	0
U.S. Corporate Debt [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	199,000,000	185,000,000
International Bonds [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member]
Fair value of plan assets	920,000,000	765,000,000
International Bonds [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	0	0
International Bonds [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	920,000,000	765,000,000
Multi-Sector [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member]
Fair value of plan assets	2,000,000	2,000,000
Multi-Sector [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	2,000,000	2,000,000
Multi-Sector [Member] | Fixed Income - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	0	0
U.S. Equity [Member] | Equity - Held Through Mutual and Pooled Funds [Member]
Fair value of plan assets	678,000,000	680,000,000
U.S. Equity [Member] | Equity - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	3,000,000	3,000,000
U.S. Equity [Member] | Equity - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	675,000,000	677,000,000
International Equity [Member] | Equity - Assets Held Directly [Member]
Fair value of plan assets	143,000,000	189,000,000
International Equity [Member] | Equity - Assets Held Directly [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	143,000,000	189,000,000
International Equity [Member] | Equity - Assets Held Directly [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	0	0
Non-U.S. Equity [Member] | Equity - Held Through Mutual and Pooled Funds [Member]
Fair value of plan assets	925,000,000	869,000,000
Non-U.S. Equity [Member] | Equity - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	1,000,000	1,000,000
Non-U.S. Equity [Member] | Equity - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	924,000,000	868,000,000
Global Equity [Member] | Equity - Held Through Mutual and Pooled Funds [Member]
Fair value of plan assets	293,000,000	252,000,000
Global Equity [Member] | Equity - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	0	0
Global Equity [Member] | Equity - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	293,000,000	252,000,000
U.S. Equity Collars [Member] | Equity - Held Through Mutual and Pooled Funds [Member]
Fair value of plan assets		29,000,000
U.S. Equity Collars [Member] | Equity - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets		0
U.S. Equity Collars [Member] | Equity - Held Through Mutual and Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets		29,000,000
Principal Plans [Member]
Fair value of plan assets	$ 5,063,000,000	$ 4,840,000,000