Fair Value Measurements Footnote (details) - Financial Instruments (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010
Financial Satement Captions
Cash	$ 258	$ 214	$ 239	$ 200
Short-term securities	3,373	3,594
Investment income accrued	717	768
Fair Value [Member]
Financial Satement Captions
Cash	258	214
Short-term securities	3,373	3,594
Investment income accrued	717	768
Other financial assets	526	552
Total financial assets	4,874	5,128
Debt	7,660	7,609
Commercial paper	100	100
Other financial liabilities	3,619	3,931
Total financial liabilities	11,379	11,640
Fair Value [Member] | Level 1 [Member]
Financial Satement Captions
Cash	258	214
Short-term securities	1,961	2,472
Total financial assets	2,219	2,686
Fair Value [Member] | Level 2 [Member]
Financial Satement Captions
Short-term securities	1,238	1,029
Total financial assets	1,238	1,029
Debt	7,345	7,057
Total financial liabilities	7,345	7,057
Fair Value [Member] | Level 3 [Member]
Financial Satement Captions
Short-term securities	174	93
Investment income accrued	717	768
Other financial assets	526	552
Total financial assets	1,417	1,413
Debt	315	552
Commercial paper	100	100
Other financial liabilities	3,619	3,931
Total financial liabilities	4,034	4,583
Carrying Value [Member]
Financial Satement Captions
Cash	258	214
Short-term securities	3,373	3,594
Investment income accrued	717	768
Other financial assets	526	552
Total financial assets	4,874	5,128
Debt	6,506	6,505
Commercial paper	100	100
Other financial liabilities	3,619	3,931
Total financial liabilities	$ 10,225	$ 10,536