Fair Value Measurement - Recurring Fair Value Measurements (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	[1],[2]	$ 36	$ 28
Total	[1]	5,947	6,090
Business Combination, Contingent Consideration, Liability	[1]	13	26
Financial and Nonfinancial Liabilities, Fair Value Disclosure	[1]	13	26
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	[2]	15	15
Total		15	15
Business Combination, Contingent Consideration, Liability		0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure		0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	[2]	0	0
Total		5,866	6,012
Business Combination, Contingent Consideration, Liability		0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure		0	0
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	[2]	21	13
Total		66	63
Business Combination, Contingent Consideration, Liability		13	26
Financial and Nonfinancial Liabilities, Fair Value Disclosure		13	26
U.S. Government and federal agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		2,469	2,888
U.S. Government and federal agency | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	[1]	2,469	2,888
U.S. Government and federal agency | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
U.S. Government and federal agency | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		2,469	2,888
U.S. Government and federal agency | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
State and municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		45	48
State and municipal | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	[1]	45	48
State and municipal | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
State and municipal | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
State and municipal | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		45	48
Residential mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	[3]	1,026	1,139
Residential mortgage-backed | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	[1]	1,026	1,139
Residential mortgage-backed | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Residential mortgage-backed | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		1,026	1,139
Residential mortgage-backed | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	[4]	2,371	1,985
Asset-backed | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	[1]	2,371	1,985
Asset-backed | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Asset-backed | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		2,371	1,985
Asset-backed | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
U.S. corporate debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		$ 0	2
U.S. corporate debt | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	[1]		2
U.S. corporate debt | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities			0
U.S. corporate debt | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities			0
U.S. corporate debt | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities			$ 2

[1] For the years ended December 31, 2019 and 2018, there were no securities transferred between levels.

[2] Other assets primarily relate to equity investments measured at fair value.

[3] All of our residential mortgage-backed securities have been issued by government-sponsored entities and are collateralized by U.S. mortgages. At December 31, 2019 and 2018, $351 million and $313 million of residential mortgage-backed securities, respectively, are pledged by the Bank as collateral to the Federal Reserve to secure Federal Reserve Discount Window advances.

[4] All of our asset-backed securities are collateralized by credit card loans.