Financial Instruments (Unrealized Gains on Available for Sale Securities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Available For Sale Securities: Special Use Funds - Equity securities [Member]
Total unrealized gains on available for sale securities
Unrealized gains on available for sale securities	$ 546	$ 612
Available For Sale Securities: Special Use Funds - U.S. Government and municipal bonds [Member]
Total unrealized gains on available for sale securities
Unrealized gains on available for sale securities	46	15
Available For Sale Securities: Special Use Funds - Corporate debt securities [Member]
Total unrealized gains on available for sale securities
Unrealized gains on available for sale securities	31	23
Available For Sale Securities: Special Use Funds - Mortgage-backed securities [Member]
Total unrealized gains on available for sale securities
Unrealized gains on available for sale securities	27	20
Available For Sale Securities: Special Use Funds - Other debt securities [Member]
Total unrealized gains on available for sale securities
Unrealized gains on available for sale securities	$ 3	$ 2