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Debt and Interest Expense - Debt Outstanding Table (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Short-term debt, carrying value [1] $ 28,000,000 $ 0
Long-term debt, carrying value [1] 4,787,381,000 3,492,712,000
WGP RCF [Member] | Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Principal 28,000,000 28,000,000
Short-term debt, carrying value 28,000,000  
Long-term debt, carrying value   28,000,000
WGP RCF [Member] | Revolving Credit Facility [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Short-term debt, fair value [2] 28,000,000  
Long-term debt, fair value [2]   28,000,000
Long Term Debt Obligations [Member]    
Debt Instrument [Line Items]    
Total long-term debt, principal 5,267,493,000 3,616,966,000
Long-term debt, carrying value 5,214,874,000 3,591,678,000
Long Term Debt Obligations [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value 4,976,815,000 3,721,143,000
Western Gas Partners, LP [Member] | WES RCF [Member] | Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Principal 220,000,000 370,000,000
Long-term debt, carrying value 220,000,000 370,000,000
Western Gas Partners, LP [Member] | WES RCF [Member] | Revolving Credit Facility [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 220,000,000 $ 370,000,000
Western Gas Partners, LP [Member] | APCWH Note Payable [Member]    
Debt Instrument [Line Items]    
Interest rate 3.04% 2.09%
Principal $ 427,493,000 $ 98,966,000
Long-term debt, carrying value 427,493,000 98,966,000
Western Gas Partners, LP [Member] | APCWH Note Payable [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value $ 427,493,000 98,966,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 2.600% Senior Notes due 2018 [Member]    
Debt Instrument [Line Items]    
Interest rate 2.60%  
Debt instrument, maturity date Aug. 15, 2018  
Principal $ 0 350,000,000
Long-term debt, carrying value 0 349,684,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 2.600% Senior Notes due 2018 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 0 350,631,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 5.375% Senior Notes due 2021 [Member]    
Debt Instrument [Line Items]    
Interest rate 5.375%  
Debt instrument, maturity date Jun. 01, 2021  
Principal $ 500,000,000 500,000,000
Long-term debt, carrying value 496,959,000 495,815,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 5.375% Senior Notes due 2021 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 515,990,000 530,647,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 4.000% Senior Notes due 2022 [Member]    
Debt Instrument [Line Items]    
Interest rate 4.00%  
Debt instrument, maturity date Jul. 01, 2022  
Principal $ 670,000,000 670,000,000
Long-term debt, carrying value 669,078,000 668,849,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 4.000% Senior Notes due 2022 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 662,109,000 684,043,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 3.950% Senior Notes due 2025 [Member]    
Debt Instrument [Line Items]    
Interest rate 3.95%  
Debt instrument, maturity date Jun. 01, 2025  
Principal $ 500,000,000 500,000,000
Long-term debt, carrying value 492,837,000 491,885,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 3.950% Senior Notes due 2025 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 466,135,000 500,885,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 4.650% Senior Notes due 2026 [Member]    
Debt Instrument [Line Items]    
Interest rate 4.65%  
Debt instrument, maturity date Jul. 01, 2026  
Principal $ 500,000,000 500,000,000
Long-term debt, carrying value 495,710,000 495,245,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 4.650% Senior Notes due 2026 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 483,994,000 520,144,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 4.500% Senior Notes due 2028 [Member]    
Debt Instrument [Line Items]    
Interest rate 4.50%  
Debt instrument, maturity date Mar. 01, 2028  
Principal $ 400,000,000 0
Long-term debt, carrying value 394,631,000 0
Western Gas Partners, LP [Member] | Senior Notes [Member] | 4.500% Senior Notes due 2028 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 377,475,000 0
Western Gas Partners, LP [Member] | Senior Notes [Member] | 4.750% Senior Notes due 2028 [Member]    
Debt Instrument [Line Items]    
Interest rate 4.75%  
Debt instrument, maturity date Aug. 15, 2028  
Principal $ 400,000,000 0
Long-term debt, carrying value 395,841,000 0
Western Gas Partners, LP [Member] | Senior Notes [Member] | 4.750% Senior Notes due 2028 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 384,370,000 0
Western Gas Partners, LP [Member] | Senior Notes [Member] | 5.450% Senior Notes due 2044 [Member]    
Debt Instrument [Line Items]    
Interest rate 5.45%  
Debt instrument, maturity date Apr. 01, 2044  
Principal $ 600,000,000 600,000,000
Long-term debt, carrying value 593,349,000 593,234,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 5.450% Senior Notes due 2044 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 522,386,000 637,827,000
Western Gas Partners, LP [Member] | Senior Notes [Member] | 5.300% Senior Notes due 2048 [Member]    
Debt Instrument [Line Items]    
Interest rate 5.30%  
Debt instrument, maturity date Mar. 01, 2048  
Principal $ 700,000,000 0
Long-term debt, carrying value 686,648,000 0
Western Gas Partners, LP [Member] | Senior Notes [Member] | 5.300% Senior Notes due 2048 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 605,327,000 0
Western Gas Partners, LP [Member] | Senior Notes [Member] | 5.500% Senior Notes due 2048 [Member]    
Debt Instrument [Line Items]    
Interest rate 5.50%  
Debt instrument, maturity date Aug. 15, 2048  
Principal $ 350,000,000 0
Long-term debt, carrying value 342,328,000 0
Western Gas Partners, LP [Member] | Senior Notes [Member] | 5.500% Senior Notes due 2048 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]    
Debt Instrument [Line Items]    
Long-term debt, fair value [2] $ 311,536,000 $ 0
[1] Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2] Fair value is measured using the market approach and Level 2 inputs.