Summary of Significant Accounting Policies - Change in Accounting Policy (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Jan. 01, 2018
Balance Sheet Related Disclosures [Abstract]
Other assets	$ 38,899		$ 34,404
Total assets	228,332		244,596
Accrued expenses and other liabilities	27,274		24,232
Retained earnings	20,911		20,553
Total liabilities and stockholders' equity	228,332		244,596
Income Statement Related Disclosures [Abstract]
Processing fees and other	191	$ 77
Total fee revenue	2,260	2,415
Income tax expense	127	129
Net income	$ 508	$ 659
Basic (in USD per share)	$ 1.20	$ 1.64
Diluted (in USD per share)	$ 1.18	$ 1.62
As Originally Reported
Balance Sheet Related Disclosures [Abstract]
Other assets			34,434
Total assets			244,626
Accrued expenses and other liabilities			24,209
Retained earnings			20,606
Total liabilities and stockholders' equity			244,626
Income Statement Related Disclosures [Abstract]
Processing fees and other	$ 169	$ 52
Total fee revenue	2,238	2,390
Income tax expense	105	102
Net income	$ 508	$ 661
Basic (in USD per share)	$ 1.20	$ 1.65
Diluted (in USD per share)	$ 1.18	$ 1.62
Effect of Change
Balance Sheet Related Disclosures [Abstract]
Retained earnings				$ (47)
Change from equity method of accounting to proportional amortization method for investments in LIHTC | Effect of Change
Balance Sheet Related Disclosures [Abstract]
Other assets			(30)
Total assets			(30)
Accrued expenses and other liabilities			23
Retained earnings			(53)
Total liabilities and stockholders' equity			$ (30)
Income Statement Related Disclosures [Abstract]
Processing fees and other	$ 22	$ 25
Total fee revenue	22	25
Income tax expense	22	27
Net income	$ 0	$ (2)
Basic (in USD per share)	$ 0	$ (0.01)
Diluted (in USD per share)	$ 0	$ 0