Other Financial Data (Sigma Fund) (Details) (USD $) In Millions, unless otherwise specified	Mar. 30, 2013	Dec. 31, 2012
Sigma Fund
Sigma Fund	$ 2,245	$ 2,133
Cash [Member]
Sigma Fund
Sigma Fund	0	149
U.S. Government, Agency and Government-sponsored Enterprise Obligations [Member]
Sigma Fund
Sigma Fund	$ 2,245	$ 1,984