Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	$ 666	$ 726
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans and leases	42	9
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans and leases	$ 42	$ 9
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	20.00%	0.00%
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	40.00%	50.00%
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	21.00%	23.00%
Level 3 [Member] | Other Investments [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments		$ 13
EBITDA Multiple [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		6.00%
EBITDA Multiple (where applicable) [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		6.00%