Leases - Components of Operating Lease Costs (Details) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2019 USD ($) branch	Dec. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease cost			$ 136
Variable lease cost			63
Short-term lease cost			4
Sublease income	[1]		(60)
Total operating lease costs, net			143
Cash paid for amounts included in the measurement of operating lease liabilities			126
ROU assets recognized for new operating lease liabilities			$ 132
Number of branches closing | branch		20
Occupancy Expense, Net [Member]
Lessee, Lease, Description [Line Items]
Impairment charge		$ 13

[1] We have entered into agreements to sublease certain office space, including agreements to receive rental income from our affiliates for rent. As owner or lessee of the properties, we have entered into agreements with these affiliates to charge them rent based on the office space utilized by their employees during the period. See Note 23, "Related Party Transactions," for further disclosure.