Escrow Deposits, Like-Kind Exchange Deposits and Trust Assets (Narrative) (Detail) - USD ($) $ in Billions	Mar. 31, 2019	Dec. 31, 2018
Other Assets [Line Items]
Escrow deposits	$ 7.7	$ 7.6
Like-kind exchange funds	2.2	2.7
First American Trust
Other Assets [Line Items]
Escrow deposits	3.8	3.6
Assets held-in-trust	$ 4.0	$ 3.6