Accumulated Other Comprehensive Income (Loss) - Details of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
TAX EFFECT
Other comprehensive income (loss), after reclassifications	$ 112.4	$ (72.4)	$ (17.0)
AFTER TAX
Other Comprehensive Income (Loss)	(44.3)	2.7	(53.0)
Unrealized (Losses) Gains on Securities Available for Sale
BEFORE TAX
Other comprehensive income (loss) before reclassifications	(70.2)	(1.8)	(94.3)
TAX EFFECT
Other comprehensive income (loss) before reclassifications	26.9	0.7	35.5
AFTER TAX
Other comprehensive income (loss) before reclassifications	(43.3)	(1.1)	(58.8)
Net Unrealized (Losses) Gains on Securities Available for Sale
BEFORE TAX
Reclassification adjustments	1.4	(0.5)	0.3
Other comprehensive income (loss), after reclassifications	(68.8)	(2.3)	(94.0)
TAX EFFECT
Reclassification adjustments	(0.5)	0.2	(0.1)
Other comprehensive income (loss), after reclassifications	26.4	0.9	35.4
AFTER TAX
Reclassification adjustments	0.9	(0.3)	0.2
Other Comprehensive Income (Loss)	(42.4)	(1.4)	(58.6)
Net Unrealized Gains (Losses) on Cash Flow Hedges
BEFORE TAX
Other comprehensive income (loss) before reclassifications	33.8	4.4	(1.2)
Reclassification adjustments	(24.5)	(1.9)	4.7
Other comprehensive income (loss), after reclassifications	9.3	2.5	3.5
TAX EFFECT
Other comprehensive income (loss) before reclassifications	(20.3)	5.9	0.2
Reclassification adjustments	9.4	0.7	(2.0)
Other comprehensive income (loss), after reclassifications	(10.9)	6.6	(1.8)
AFTER TAX
Other comprehensive income (loss) before reclassifications	13.5	10.3	(1.0)
Reclassification adjustments	(15.1)	(1.2)	2.7
Other Comprehensive Income (Loss)	(1.6)	9.1	1.7
Net Foreign Currency Adjustments
BEFORE TAX
Other comprehensive income (loss) before reclassifications	156.5	(126.5)	(101.5)
Other comprehensive income (loss), after reclassifications	(64.7)	80.6	28.4
TAX EFFECT
Other comprehensive income (loss) before reclassifications	(3.1)	(3.1)	4.9
Other comprehensive income (loss), after reclassifications	81.4	(81.5)	(44.3)
AFTER TAX
Other comprehensive income (loss) before reclassifications	153.4	(129.6)	(96.6)
Other Comprehensive Income (Loss)	16.7	(0.9)	(15.9)
Long-Term Intra-Entity Foreign Currency Transaction Losses
BEFORE TAX
Other comprehensive income (loss) before reclassifications	2.0	(5.3)	(18.7)
TAX EFFECT
Other comprehensive income (loss) before reclassifications	(0.7)	2.0	7.1
AFTER TAX
Other comprehensive income (loss) before reclassifications	1.3	(3.3)	(11.6)
Net Investment Hedge Gains (Losses)
BEFORE TAX
Other comprehensive income (loss) before reclassifications	(223.2)	212.4	148.6
TAX EFFECT
Other comprehensive income (loss) before reclassifications	85.2	(80.4)	(56.3)
AFTER TAX
Other comprehensive income (loss) before reclassifications	(138.0)	132.0	92.3
Net Pension and Other Postretirement Benefit Adjustments
BEFORE TAX
Other comprehensive income (loss) before reclassifications	(58.4)	(31.1)	(12.2)
Reclassification adjustments	25.9	25.4	38.3
Other comprehensive income (loss), after reclassifications	(32.5)	(5.7)	26.1
TAX EFFECT
Other comprehensive income (loss) before reclassifications	25.4	11.2	8.2
Reclassification adjustments	(9.9)	(9.6)	(14.5)
Other comprehensive income (loss), after reclassifications	15.5	1.6	(6.3)
AFTER TAX
Other comprehensive income (loss) before reclassifications	(33.0)	(19.9)	(4.0)
Reclassification adjustments	16.0	15.8	23.8
Other Comprehensive Income (Loss)	$ (17.0)	$ (4.1)	$ 19.8