Business Segment Information - Segments' Total Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Segments’ total assets
Total assets	$ 2,619,954	$ 2,434,079	$ 2,377,164
Operating Segments
Segments’ total assets
Total assets	2,378,652		2,198,574
ALM activities
Segments’ total assets
Total assets	840,187		671,751
Elimination of segment asset allocations to match liabilities
Segments’ total assets
Total assets	(665,795)		(566,812)
Other
Segments’ total assets
Total assets	$ 66,910		$ 73,651