Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total Revenues	$ 126	$ 125	$ 121	$ 131	$ 143	$ 153	$ 129	$ 100	$ 503	$ 525	$ 470
Income Before Income Taxes	144	146	119	137	148	155	115	65	546	483	392
Net income	144	146	119	137	147	155	115	65	546	482	392
Net Income Attributable to the Partnership	140	141	115	132	140	149	111	64	528	464	295
Limited Partners’ Interest in Net Income Attributable to the Partnership	$ 86	$ 105	$ 85	$ 105	$ 102	$ 112	$ 79	$ 37	$ 381	$ 330	$ 231
Net income per Limited Partner Unit - Basic and Diluted (in dollars per share)	$ 0.37	$ 0.45	$ 0.38	$ 0.47	$ 0.45	$ 0.50	$ 0.35	$ 0.18