Partners' Capital and Distributions - Activity for Series A and B Preferred Units and Common Units (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Series A Preferred Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance, beginning of period (in units)	71,090,468
Balance, end of period (in units)	71,090,468	71,090,468
Series B Preferred Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance, beginning of period (in units)	800,000
Balance, end of period (in units)	800,000	800,000
Common Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance, beginning of period (in units)	728,028,576
Balance, end of period (in units)	722,380,416	728,028,576
Limited Partners | Series A Preferred Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance, beginning of period (in units)	71,090,468	71,090,468	69,696,542
Issuances of Series A preferred units in connection with in-kind distributions (in units)			1,393,926
Balance, end of period (in units)	71,090,468	71,090,468	71,090,468
Limited Partners | Series B Preferred Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance, beginning of period (in units)	800,000	800,000	800,000
Balance, end of period (in units)	800,000	800,000	800,000
Limited Partners | Common Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance, beginning of period (in units)	728,028,576	726,361,924	725,189,138
Repurchase and cancellation of common units under the Common Equity Repurchase Program (in shares)	(6,222,748)
Issuance of common units under equity-indexed compensation plans (in units)	574,588	1,666,652	1,172,786
Balance, end of period (in units)	722,380,416	728,028,576	726,361,924