Fair Value Measurement (Unaudited) (Details) (USD $) In Millions	Sep. 30, 2011
Fair Value, Measurements, Recurring [Member] | Money market funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Cash equivalents:
Cash equivalents	$ 4,828
Trust assets (current and long-term):
Trust assets	11
Available-for-sale securities:
Available-for-sale securities	2
Fair Value, Measurements, Recurring [Member] | Money market funds [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents:
Cash equivalents	4,828
Trust assets (current and long-term):
Trust assets	11
Available-for-sale securities:
Available-for-sale securities	2
Fair Value, Measurements, Recurring [Member] | Money market funds [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents:
Cash equivalents	0
Trust assets (current and long-term):
Trust assets	0
Available-for-sale securities:
Available-for-sale securities	0
Fair Value, Measurements, Recurring [Member] | Money market funds [Member] | Fair Value, Inputs, Level 3 [Member]
Cash equivalents:
Cash equivalents	0
Trust assets (current and long-term):
Trust assets	0
Available-for-sale securities:
Available-for-sale securities	0
Fair Value, Measurements, Recurring [Member] | Time deposits [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Cash equivalents:
Cash equivalents	201
Available-for-sale securities:
Available-for-sale securities	15
Fair Value, Measurements, Recurring [Member] | Time deposits [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents:
Cash equivalents	201
Available-for-sale securities:
Available-for-sale securities	15
Fair Value, Measurements, Recurring [Member] | Time deposits [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents:
Cash equivalents	0
Available-for-sale securities:
Available-for-sale securities	0
Fair Value, Measurements, Recurring [Member] | Time deposits [Member] | Fair Value, Inputs, Level 3 [Member]
Cash equivalents:
Cash equivalents	0
Available-for-sale securities:
Available-for-sale securities	0
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Cash equivalents:
Cash equivalents	5,029
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents:
Cash equivalents	5,029
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents:
Cash equivalents	0
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Cash equivalents:
Cash equivalents	0
Fair Value, Measurements, Recurring [Member] | U.S. core fixed income funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Trust assets (current and long-term):
Trust assets	46
Fair Value, Measurements, Recurring [Member] | U.S. core fixed income funds [Member] | Fair Value, Inputs, Level 1 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | U.S. core fixed income funds [Member] | Fair Value, Inputs, Level 2 [Member]
Trust assets (current and long-term):
Trust assets	46
Fair Value, Measurements, Recurring [Member] | U.S. core fixed income funds [Member] | Fair Value, Inputs, Level 3 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Government mortgage-backed securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Trust assets (current and long-term):
Trust assets	40
Fair Value, Measurements, Recurring [Member] | Government mortgage-backed securities [Member] | Fair Value, Inputs, Level 1 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Government mortgage-backed securities [Member] | Fair Value, Inputs, Level 2 [Member]
Trust assets (current and long-term):
Trust assets	40
Fair Value, Measurements, Recurring [Member] | Government mortgage-backed securities [Member] | Fair Value, Inputs, Level 3 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Trust assets (current and long-term):
Trust assets	18
Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Trust assets (current and long-term):
Trust assets	18
Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Trust assets (current and long-term):
Trust assets	15
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member] | Fair Value, Inputs, Level 1 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member] | Fair Value, Inputs, Level 2 [Member]
Trust assets (current and long-term):
Trust assets	15
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member] | Fair Value, Inputs, Level 3 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Government bonds and notes [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Trust assets (current and long-term):
Trust assets	22
Fair Value, Measurements, Recurring [Member] | Government bonds and notes [Member] | Fair Value, Inputs, Level 1 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Government bonds and notes [Member] | Fair Value, Inputs, Level 2 [Member]
Trust assets (current and long-term):
Trust assets	22
Fair Value, Measurements, Recurring [Member] | Government bonds and notes [Member] | Fair Value, Inputs, Level 3 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Trust assets (current and long-term):
Trust assets	1
Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Trust assets (current and long-term):
Trust assets	1
Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Trust assets (current and long-term):
Trust assets	0
Fair Value, Measurements, Recurring [Member] | Equity securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Available-for-sale securities:
Available-for-sale securities	8
Fair Value, Measurements, Recurring [Member] | Equity securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities:
Available-for-sale securities	8
Fair Value, Measurements, Recurring [Member] | Equity securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities:
Available-for-sale securities	0
Fair Value, Measurements, Recurring [Member] | Equity securities [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale securities:
Available-for-sale securities	0
Fair Value, Measurements, Recurring [Member] | Embedded derivatives in provisional sales/purchases contracts [Member] | Fair Value, Inputs, Level 2 [Member]
Derivatives (Assets):
Derivative assets	0
Fair Value, Measurements, Recurring [Member] | Embedded derivatives in provisional sales/purchases contracts [Member] | Fair Value, Inputs, Level 3 [Member]
Derivatives (Assets):
Derivative assets	0
Fair Value, Measurements, Recurring [Member] | Atlantic Copper's copper forward contracts [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives (Liabilities):
Derivative liabilities	(1)
Fair Value, Measurements, Recurring [Member] | Atlantic Copper's copper forward contracts [Member] | Fair Value, Inputs, Level 1 [Member]
Derivatives (Liabilities):
Derivative liabilities	(1)
Fair Value, Measurements, Recurring [Member] | Atlantic Copper's copper forward contracts [Member] | Fair Value, Inputs, Level 2 [Member]
Derivatives (Liabilities):
Derivative liabilities	0
Fair Value, Measurements, Recurring [Member] | Atlantic Copper's copper forward contracts [Member] | Fair Value, Inputs, Level 3 [Member]
Derivatives (Liabilities):
Derivative liabilities	0
Fair Value, Measurements, Recurring [Member] | Embedded derivatives in provisional sales/purchases contracts [Member] | Fair Value, Inputs, Level 2 [Member]
Derivatives (Liabilities):
Derivative liabilities	0
Fair Value, Measurements, Recurring [Member] | Embedded derivatives in provisional sales/purchases contracts [Member] | Fair Value, Inputs, Level 3 [Member]
Derivatives (Liabilities):
Derivative liabilities	0
Fair Value, Measurements, Recurring [Member] | FMC's Copper Futures and Swap Contracts [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives (Liabilities):
Derivative liabilities	(54)
Fair Value, Measurements, Recurring [Member] | FMC's Copper Futures and Swap Contracts [Member] | Fair Value, Inputs, Level 1 [Member]
Derivatives (Liabilities):
Derivative liabilities	(54)
Fair Value, Measurements, Recurring [Member] | FMC's Copper Futures and Swap Contracts [Member] | Fair Value, Inputs, Level 2 [Member]
Derivatives (Liabilities):
Derivative liabilities	0
Fair Value, Measurements, Recurring [Member] | FMC's Copper Futures and Swap Contracts [Member] | Fair Value, Inputs, Level 3 [Member]
Derivatives (Liabilities):
Derivative liabilities	0
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Trust assets (current and long-term):
Trust assets	153
Available-for-sale securities:
Available-for-sale securities	25
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Trust assets (current and long-term):
Trust assets	11
Available-for-sale securities:
Available-for-sale securities	25
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Trust assets (current and long-term):
Trust assets	142
Available-for-sale securities:
Available-for-sale securities	0
Derivatives (Assets):
Total assets	142
Derivatives (Liabilities):
Derivative liabilities	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Trust assets (current and long-term):
Trust assets	0
Available-for-sale securities:
Available-for-sale securities	0
Derivatives (Assets):
Total assets	0
Derivatives (Liabilities):
Derivative liabilities	0
Embedded derivatives in provisional sales/purchases contracts [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives (Assets):
Derivative assets	179
Embedded derivatives in provisional sales/purchases contracts [Member] | Fair Value, Inputs, Level 1 [Member]
Derivatives (Assets):
Derivative assets	179
Embedded derivatives in provisional sales/purchases contracts [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives (Liabilities):
Derivative liabilities	(581)
Embedded derivatives in provisional sales/purchases contracts [Member] | Fair Value, Inputs, Level 1 [Member]
Derivatives (Liabilities):
Derivative liabilities	(581)
Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives (Assets):
Total assets	5,386
Derivatives (Liabilities):
Derivative liabilities	(636)
Fair Value, Inputs, Level 1 [Member]
Derivatives (Assets):
Total assets	5,244
Derivatives (Liabilities):
Derivative liabilities	$ (636)