Long-Term Debt (Detail) - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018 |
Debt Instrument [Line Items] | | |
Credit Facility | $ 0 | $ 0 |
Finance lease obligations | 162 | 163 |
Total debt | 10,256 | 9,347 |
Less: Current portion of long-term debt | (231) | (833) |
Long-term debt, noncurrent | 10,025 | 8,514 |
Series K Notes, interest rate of 3.0%, face amount of $600, matured March 1, 2019 (effective interest rate of 4.4%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 0 | 600 |
Series L Notes, interest rate of 3.3%, face amount of $350, maturing September 15, 2022 (effective interest rate of 3.4%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 349 | 349 |
Series M Notes, interest rate of 3.4%, face amount of $350, maturing October 15, 2020 (effective interest rate of 3.6%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 349 | 349 |
Series N Notes, interest rate of 3.1%, face amount of $400, maturing October 15, 2021 (effective interest rate of 3.4%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 398 | 397 |
Series O Notes, interest rate of 2.9%, face amount of $450, maturing March 1, 2021 (effective interest rate of 3.1%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 448 | 448 |
Series P Notes, interest rate of 3.8%, face amount of $350, maturing October 1, 2025 (effective interest rate of 4.0%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 345 | 345 |
Series Q Notes, interest rate of 2.3%, face amount of $750, maturing January 15, 2022 (effective interest rate of 2.5%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 745 | 745 |
Series R Notes, interest rate of 3.1%, face amount of $750, maturing June 15, 2026 (effective interest rate of 3.3%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 744 | 743 |
Series T Notes, interest rate of 7.2%, face amount of $181, maturing December 1, 2019 (effective interest rate of 2.3%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 186 | 188 |
Series U Notes, interest rate of 3.1%, face amount of $291, maturing February 15, 2023 (effective interest rate of 3.1%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 291 | 291 |
Series V Notes, interest rate of 3.8%, face amount of $318, maturing March 15, 2025 (effective interest rate of 2.8%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 334 | 335 |
Series W Notes, interest rate of 4.5%, face amount of $278, maturing October 1, 2034 (effective interest rate of 4.1%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 292 | 292 |
Series X Notes, interest rate of 4.0%, face amount of $450, maturing April 15, 2028 (effective interest rate of 4.2%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 443 | 443 |
Series Y Notes, floating rate, face amount of $550, maturing December 1, 2020 (effective interest rate of 3.2% at March 31, 2019) | | |
Debt Instrument [Line Items] | | |
Senior notes | 548 | 547 |
Series Z Notes, interest rate of 4.2%, face amount of $350, maturing December 1, 2023 (effective interest rate of 4.4%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 347 | 347 |
Series AA Notes, interest rate of 4.7%, face amount of $300, maturing December 1, 2028 (effective interest rate of 4.8%) | | |
Debt Instrument [Line Items] | | |
Senior notes | 297 | 297 |
Series BB Notes, floating rate, face amount of $300, maturing March 8, 2021 (effective interest rate of 3.2% at March 31, 2019) | | |
Debt Instrument [Line Items] | | |
Senior notes | 298 | 0 |
Series CC Notes, interest rate of 3.6%, face amount of $550, maturing April 15, 2024 (effective interest rate of 3.9%) | | |
Debt Instrument [Line Items] | | |
Senior notes | $ 550 | 0 |
Senior Notes | Series K Notes, interest rate of 3.0%, face amount of $600, matured March 1, 2019 (effective interest rate of 4.4%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 3.00% | |
Senior notes, face amount | $ 600 | |
Effective interest rate | 4.40% | |
Senior Notes | Series L Notes, interest rate of 3.3%, face amount of $350, maturing September 15, 2022 (effective interest rate of 3.4%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 3.30% | |
Senior notes, face amount | $ 350 | |
Effective interest rate | 3.40% | |
Senior Notes | Series M Notes, interest rate of 3.4%, face amount of $350, maturing October 15, 2020 (effective interest rate of 3.6%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 3.40% | |
Senior notes, face amount | $ 350 | |
Effective interest rate | 3.60% | |
Senior Notes | Series N Notes, interest rate of 3.1%, face amount of $400, maturing October 15, 2021 (effective interest rate of 3.4%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 3.10% | |
Senior notes, face amount | $ 400 | |
Effective interest rate | 3.40% | |
Senior Notes | Series O Notes, interest rate of 2.9%, face amount of $450, maturing March 1, 2021 (effective interest rate of 3.1%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 2.90% | |
Senior notes, face amount | $ 450 | |
Effective interest rate | 3.10% | |
Senior Notes | Series P Notes, interest rate of 3.8%, face amount of $350, maturing October 1, 2025 (effective interest rate of 4.0%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 3.80% | |
Senior notes, face amount | $ 350 | |
Effective interest rate | 4.00% | |
Senior Notes | Series Q Notes, interest rate of 2.3%, face amount of $750, maturing January 15, 2022 (effective interest rate of 2.5%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 2.30% | |
Senior notes, face amount | $ 750 | |
Effective interest rate | 2.50% | |
Senior Notes | Series R Notes, interest rate of 3.1%, face amount of $750, maturing June 15, 2026 (effective interest rate of 3.3%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 3.10% | |
Senior notes, face amount | $ 750 | |
Effective interest rate | 3.30% | |
Senior Notes | Series T Notes, interest rate of 7.2%, face amount of $181, maturing December 1, 2019 (effective interest rate of 2.3%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 7.20% | |
Senior notes, face amount | $ 181 | |
Effective interest rate | 2.30% | |
Senior Notes | Series U Notes, interest rate of 3.1%, face amount of $291, maturing February 15, 2023 (effective interest rate of 3.1%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 3.10% | |
Senior notes, face amount | $ 291 | |
Effective interest rate | 3.10% | |
Senior Notes | Series V Notes, interest rate of 3.8%, face amount of $318, maturing March 15, 2025 (effective interest rate of 2.8%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 3.80% | |
Senior notes, face amount | $ 318 | |
Effective interest rate | 2.80% | |
Senior Notes | Series W Notes, interest rate of 4.5%, face amount of $278, maturing October 1, 2034 (effective interest rate of 4.1%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 4.50% | |
Senior notes, face amount | $ 278 | |
Effective interest rate | 4.10% | |
Senior Notes | Series X Notes, interest rate of 4.0%, face amount of $450, maturing April 15, 2028 (effective interest rate of 4.2%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 4.00% | |
Senior notes, face amount | $ 450 | |
Effective interest rate | 4.20% | |
Senior Notes | Series Y Notes, floating rate, face amount of $550, maturing December 1, 2020 (effective interest rate of 3.2% at March 31, 2019) | | |
Debt Instrument [Line Items] | | |
Senior notes, face amount | $ 550 | |
Effective interest rate | 3.20% | |
Senior Notes | Series Z Notes, interest rate of 4.2%, face amount of $350, maturing December 1, 2023 (effective interest rate of 4.4%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 4.20% | |
Senior notes, face amount | $ 350 | |
Effective interest rate | 4.40% | |
Senior Notes | Series AA Notes, interest rate of 4.7%, face amount of $300, maturing December 1, 2028 (effective interest rate of 4.8%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 4.70% | |
Senior notes, face amount | $ 300 | |
Effective interest rate | 4.80% | |
Senior Notes | Series BB Notes, floating rate, face amount of $300, maturing March 8, 2021 (effective interest rate of 3.2% at March 31, 2019) | | |
Debt Instrument [Line Items] | | |
Senior notes, face amount | $ 300 | |
Effective interest rate | 3.20% | |
Senior Notes | Series CC Notes, interest rate of 3.6%, face amount of $550, maturing April 15, 2024 (effective interest rate of 3.9%) | | |
Debt Instrument [Line Items] | | |
Interest rate | 3.60% | |
Senior notes, face amount | $ 550 | |
Effective interest rate | 3.90% | |
Commercial paper | | |
Debt Instrument [Line Items] | | |
Commercial paper | $ 2,911 | 2,245 |
Other | | |
Debt Instrument [Line Items] | | |
Other | $ 219 | $ 223 |