Selected Quarterly Financial Data - Reclassified Amounts (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	[1]	Dec. 31, 2016	[1]	Dec. 31, 2015	[1]
Condensed Income Statements, Captions [Line Items]
Total other revenues	$ 458	$ 393	$ 558	$ 593	$ 282	$ 338	$ 307	$ 477	$ 2,002		$ 1,404		$ 1,735
Operating expenses	$ 903	820	849	819	899	821	837	741	$ 3,391		$ 3,298	[2]	$ 3,284	[2]
Reclassified Amount [Member]
Condensed Income Statements, Captions [Line Items]
Total other revenues		25	29	32	25	18	14	15
Operating expenses		$ 25	$ 29	$ 32	$ 25	$ 18	$ 14	$ 15

[1] Expenses for the segments include fully apportioned corporate overhead expenses.

[2] In 2017, we changed our presentation for certain cost reimbursements that were previously netted as an offset to affiliate expense. We now present these reimbursements gross in affiliate income. As a result, we have reclassified prior year amounts in order to conform to the current year presentation, which increased both RBWM other operating income and RBWM operating expenses $11 million during the year ended December 31, 2016 and also increased both GB&M other operating income and GB&M operating expenses $61 million and $63 million during the years ended December 31, 2016 and 2015, respectively. See Note 21, "Related Party Transactions," in the accompanying consolidated financial statements for additional information.