Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Debt Instrument [Line Items]
Estimated fair value of total long-term debt, excluding capitalized lease obligations	$ 12,086		$ 6,787
Recorded book values of total long-term debt, excluding capitalized lease obligations	11,786		6,516
Additions to long-term debt	5,500	5
3-year floating-rate due 2017 [Member]
Debt Instrument [Line Items]
Additions to long-term debt	750
Debt maturity	Mar. 15, 2017
5-year floating-rate due 2019 [Member]
Debt Instrument [Line Items]
Additions to long-term debt	500
Debt maturity	Mar. 15, 2019
0.921% long-term debt due 2017 [Member]
Debt Instrument [Line Items]
Additions to long-term debt	1,500
Interest rate	0.921%
Debt maturity	Mar. 15, 2017
1.819% long-term debt due 2019 [Member]
Debt Instrument [Line Items]
Additions to long-term debt	1,750
Interest rate	1.819%
Debt maturity	Mar. 15, 2019
3.176 long-term debt due 2024 [Member]
Debt Instrument [Line Items]
Additions to long-term debt	1,000
Interest rate	3.176%
Debt maturity	Mar. 15, 2024
Level 1 [Member]
Debt Instrument [Line Items]
Estimated fair value of total long-term debt, excluding capitalized lease obligations	11,142
Level 2 [Member]
Debt Instrument [Line Items]
Estimated fair value of total long-term debt, excluding capitalized lease obligations	880
Level 3 [Member]
Debt Instrument [Line Items]
Estimated fair value of total long-term debt, excluding capitalized lease obligations	$ 64