Notes Payable, Other and Short-term Borrowings - Summary Notes Payable, Other and Short-term Borrowings (Parenthetical) (Detail)	Sep. 30, 2018	Jul. 24, 2018	Dec. 31, 2017	May 27, 2016
8.125% Senior Notes Due 2042 [Member]
Debt Instrument [Line Items]
Stated interest rate	8.125%		8.125%
5.375% Senior Notes Due 2019 [Member]
Debt Instrument [Line Items]
Stated interest rate	5.375%		5.375%
8.375% Senior Notes Due July 2018 [Member]
Debt Instrument [Line Items]
Stated interest rate	8.375%		8.375%
5.125% Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Stated interest rate	5.125%		5.125%	5.125%
5.375% Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Stated interest rate	5.375%	5.375%