Escrow Deposits, Like-Kind Exchange Deposits and Trust Assets (Narrative) (Detail) - USD ($) $ in Billions	Mar. 31, 2016	Dec. 31, 2015
Other Assets [Line Items]
Escrow deposits	$ 7.0	$ 6.6
Like-kind exchange funds	2.1	2.8
First American Trust
Other Assets [Line Items]
Escrow deposits	2.6
Trust assets	$ 2.9	$ 3.0