Fair Value of Financial Instruments (Details) - Fair Value, Inputs, Level 2	Sep. 30, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed rate senior notes carrying amount	$ 4,300,000,000
$400 million 1.850% senior notes due 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	400,000,000
Face value of debt	$ 400,000,000
Interest rate on senior notes	1.85%
$800 million 2.050% senior notes due 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 802,000,000
Face value of debt	$ 800,000,000
Interest rate on senior notes	2.05%
$500 million 6.250% senior notes due 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 539,000,000
Face value of debt	$ 500,000,000
Interest rate on senior notes	6.25%
$600 million 3.000% senior notes due 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 612,000,000
Face value of debt	$ 600,000,000
Interest rate on senior notes	3.00%
$500 million 2.800% senior notes due 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 504,000,000
Face value of debt	$ 500,000,000
Interest rate on senior notes	2.80%
$500 million 3.125% senior notes due 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 513,000,000
Face value of debt	$ 500,000,000
Interest rate on senior notes	3.125%
$300 million 3.850% senior notes due 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 311,000,000
Face value of debt	$ 300,000,000
Interest rate on senior notes	3.85%
$700 million 3.800% senior notes due 2026
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 723,000,000
Face value of debt	$ 700,000,000
Interest rate on senior notes	3.80%