Escrow Deposits, Like-Kind Exchange Deposits and Trust Assets (Narrative) (Detail) - USD ($)
$ in Billions
Jun. 30, 2016
Dec. 31, 2015
Other Assets [Line Items]    
Escrow deposits $ 8.0 $ 6.6
Like-kind exchange funds 2.2 2.8
First American Trust    
Other Assets [Line Items]    
Escrow deposits 3.0 2.6
Trust assets $ 3.1 $ 3.0