Variable Interest Entities - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Investments in LIHTC operating partnerships	$ 248,000,000	$ 230,000,000
Total Liabilities	2,000,000	4,000,000
Impairment expense related to tax reform	168,000,000
Other expense	460,000,000	558,000,000	$ 530,000,000
LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Investments in LIHTC operating partnerships	5,932,000,000	6,003,000,000
Total Liabilities	2,569,000,000	2,943,000,000
LIHTC Investments [Member] | Qualified affordable housing projects investment [Member]
Variable Interest Entity [Line Items]
Total Liabilities	532,000,000	476,000,000
Accrued Income And Other Assets [Member] | LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Investments in LIHTC operating partnerships	1,400,000,000	1,300,000,000
Investments [Member] | LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Amortization of investment	170,000,000	172,000,000
Tax credit of investment	166,000,000	171,000,000
Impairment expense related to tax reform		12,000,000
Other expense		3,000,000
Investments [Member] | Guaranteed Funds [Member]
Variable Interest Entity [Line Items]
Assets that can only be used to settle entities' obligations	0	4,000,000
Variable interest entity, liabilities	0	0
Fair Value, Measurements, Recurring [Member]
Variable Interest Entity [Line Items]
Other investments	$ 115,000,000	$ 144,000,000