Available-for-sale investments (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	$ 18,847	$ 17,107
Gross unrealized gains	209	256
Gross unrealized losses	(19)	(38)
Estimated fair value	19,037	17,325
US Treasury securities [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	2,896	5,044
Gross unrealized gains	13	50
Gross unrealized losses	(2)	(14)
Estimated fair value	2,907	5,080
Other government related debt securities - Obligations of U.S. government agencies and FDIC guaranteed bank debt [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	1,537	2,158
Gross unrealized gains	22	51
Gross unrealized losses	0	(1)
Estimated fair value	1,559	2,208
Other government related debt securities - Foreign and other [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	795	837
Gross unrealized gains	17	16
Gross unrealized losses	0	(1)
Estimated fair value	812	852
Corporate debt securities - Financial [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	2,887	2,252
Gross unrealized gains	61	53
Gross unrealized losses	(4)	(9)
Estimated fair value	2,944	2,296
Corporate debt securities - Industrial [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	2,963	2,441
Gross unrealized gains	77	71
Gross unrealized losses	(4)	(5)
Estimated fair value	3,036	2,507
Corporate debt securities - Other [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	342	307
Gross unrealized gains	12	10
Gross unrealized losses	0	(1)
Estimated fair value	354	316
Mortgage and asset backed securities [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	1,541	841
Gross unrealized gains	7	5
Gross unrealized losses	(4)	(5)
Estimated fair value	1,544	841
Money market mutual funds [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	5,677	3,030
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	5,677	3,030
Other short-term interest bearing securities [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	157	147
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	157	147
Total debt securities [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	18,795	17,057
Gross unrealized gains	209	256
Gross unrealized losses	(14)	(36)
Estimated fair value	18,990	17,277
Equity securities [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	52	50
Gross unrealized gains	0	0
Gross unrealized losses	(5)	(2)
Estimated fair value	$ 47	$ 48