Debt - Short-term and Long-term Debt (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Notes due 2016 2.75% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2016 2.75% Interest [Member] Uncollateralized Debt [Member]	Nov. 10, 2011 Notes due 2016 2.75% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2017 5.375% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2017 5.375% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2018 6.35% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2018 6.35% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2019 8.5% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2019 8.5% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2020 4.375% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2020 4.375% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2020 5.125% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2020 5.125% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2021 6.37% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2021 6.37% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes Due 2021 4.5% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes Due 2021 4.5% Interest [Member] Uncollateralized Debt [Member]	Mar. 31, 2011 Notes Due 2021 4.5% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2022 4% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2022 4% Interest [Member] Uncollateralized Debt [Member]	Nov. 10, 2011 Notes due 2022 4% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2023 7.65% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2023 7.65% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2023 8.3% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2023 8.3% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Debentures due 2027 7.875% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Debentures due 2027 7.875% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Step Down Notes Due 2033 8.3% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Step Down Notes Due 2033 8.3% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2036 6.15% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2036 6.15% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes Due 2041 5.875% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes Due 2041 5.875% Interest [Member] Uncollateralized Debt [Member]	Mar. 31, 2011 Notes Due 2041 5.875% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Notes due 2042 5.375% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Notes due 2042 5.375% Interest [Member] Uncollateralized Debt [Member]	Nov. 10, 2011 Notes due 2042 5.375% Interest [Member] Uncollateralized Debt [Member]	Dec. 31, 2013 Other Long Term Debt [Member] Uncollateralized Debt [Member]	Dec. 31, 2012 Other Long Term Debt [Member] Uncollateralized Debt [Member]
Debt Disclosure [Abstract]
Commercial paper	$ 100	$ 200
Current maturities of long-term debt	41	1
Other	92	0
Total short-term debt	233	201
Debt Instrument [Line Items]
Long-term debt	$ 5,014	$ 4,986	$ 600	$ 600	$ 600	$ 250	$ 250	$ 131	$ 131	$ 251	$ 251	$ 249	$ 249	$ 299	$ 299	$ 78	$ 78	$ 299	$ 299	$ 298	$ 744	$ 743	$ 743	$ 100	$ 100	$ 17	$ 17	$ 300	$ 300	$ 83	$ 83	$ 500	$ 500	$ 298	$ 298	$ 298	$ 750	$ 750	$ 750	$ 65	$ 38
Stated interest rate			2.75%	2.75%	2.75%	5.375%	5.375%	6.35%	6.35%	8.50%	8.50%	4.375%	4.375%	5.125%	5.125%	6.37%	6.37%	4.50%	4.50%	4.50%	4.00%	4.00%	4.00%	7.65%	7.65%	8.30%	8.30%	7.875%	7.875%	8.30%	8.30%	6.15%	6.15%	5.875%	5.875%	5.875%	5.375%	5.375%	5.375%