Financial Instruments (Gross Unrealized Losses and Fair Values for Investments in Unrealized Loss Position) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	$ 14,300	$ 4,157
Less than 12 Months, Unrealized Loss	(326)	(25)
12 Months or Greater, Fair Value	719	102
12 Months or Greater, Unrealized Loss	(32)	(5)
Total Fair Value	15,019	4,259
Total Unrealized Loss	(358)	(30)
U.S. government notes
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	4,404	842
Less than 12 Months, Unrealized Loss	(37)	(1)
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Loss	0	0
Total Fair Value	4,404	842
Total Unrealized Loss	(37)	(1)
U.S. government agencies
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	496
Less than 12 Months, Unrealized Loss	(3)
12 Months or Greater, Fair Value	0
12 Months or Greater, Unrealized Loss	0
Total Fair Value	496
Total Unrealized Loss	(3)
Foreign government bonds
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	899	509
Less than 12 Months, Unrealized Loss	(23)	(2)
12 Months or Greater, Fair Value	83	12
12 Months or Greater, Unrealized Loss	(3)	(1)
Total Fair Value	982	521
Total Unrealized Loss	(26)	(3)
Municipal securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	1,210	686
Less than 12 Months, Unrealized Loss	(32)	(6)
12 Months or Greater, Fair Value	99	9
12 Months or Greater, Unrealized Loss	(4)	0
Total Fair Value	1,309	695
Total Unrealized Loss	(36)	(6)
Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	2,583	820
Less than 12 Months, Unrealized Loss	(62)	(10)
12 Months or Greater, Fair Value	69	81
12 Months or Greater, Unrealized Loss	(5)	(4)
Total Fair Value	2,652	901
Total Unrealized Loss	(67)	(14)
Agency residential mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	4,065	1,300
Less than 12 Months, Unrealized Loss	(167)	(6)
12 Months or Greater, Fair Value	468	0
12 Months or Greater, Unrealized Loss	(20)	0
Total Fair Value	4,533	1,300
Total Unrealized Loss	(187)	(6)
Asset-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	643
Less than 12 Months, Unrealized Loss	(2)
12 Months or Greater, Fair Value	0
12 Months or Greater, Unrealized Loss	0
Total Fair Value	643
Total Unrealized Loss	$ (2)