Fair Value of Financial Instruments (Details) - Senior Notes - Fair Value, Inputs, Level 2	Mar. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed rate senior notes carrying amount	$ 4,100,000,000
$600 3.000% senior notes due 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	602,000,000
Face value of debt	$ 600,000,000
Interest rate on senior notes	3.00%
$500 2.800% senior notes due 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 499,000,000
Face value of debt	$ 500,000,000
Interest rate on senior notes	2.80%
$500 3.125% senior notes due 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 503,000,000
Face value of debt	$ 500,000,000
Interest rate on senior notes	3.125%
$700 3.650% senior notes due 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 716,000,000
Face value of debt	$ 700,000,000
Interest rate on senior notes	3.65%
$300 3.850% senior notes due 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 308,000,000
Face value of debt	$ 300,000,000
Interest rate on senior notes	3.85%
$700 3.800% senior notes due 2026
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 708,000,000
Face value of debt	$ 700,000,000
Interest rate on senior notes	3.80%
$800 4.200% senior notes due 2028
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 831,000,000
Face value of debt	$ 800,000,000
Interest rate on senior notes	4.20%