Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Millions |
12 Months Ended | ||||
---|---|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Jan. 01, 2018 |
Dec. 31, 2014 |
|
New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |||||
Increase in investments in unconsolidated entities | $ 2,756 | $ 2,343 | $ 2,027 | ||
Increase in partners' capital | 12,358 | 10,707 | 9,234 | $ 9,381 | |
Cash outflow reclassed from operating activities | 2,496 | 718 | 1,347 | ||
Cash outflow reclassed to financing activities | $ 940 | (571) | (813) | ||
ASU 2016-09 | |||||
New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |||||
Cash outflow reclassed from operating activities | 7 | 14 | |||
Cash outflow reclassed to financing activities | $ 7 | $ 14 | |||
Subsequent Event | ASU 2017-05 | |||||
New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |||||
Increase in investments in unconsolidated entities | $ 110 | ||||
Increase in partners' capital | $ 110 |