Comprehensive Income - AOCI (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period		$ 11,270,789	$ 13,870,723	$ 13,386,589	$ 13,512,529
Net current period other comprehensive income		(38,791)	52,501	366,446	288,293
Balance, end of period		11,394,964	14,101,618	11,394,964	14,101,618
Cumulative Effect, Period of Adoption, Adjustment
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				(150,213)	3,460	[1]
Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				13,236,376	13,515,989
Total
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period		404,165	13,508	(1,072)	(186,848)
Other comprehensive income (loss) before reclassifications				438,414	298,896
Amounts reclassified from accumulated other comprehensive (loss) income				(71,968)	(10,603)
Net current period other comprehensive income		(38,791)	52,501	366,446	288,293
Balance, end of period		365,374	66,009	365,374	66,009
Total | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period	[1],[2]				(35,436)
Total | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				(1,072)	(222,284)
Unrealized Gains (Losses) on Debt Securities Available for Sale and Transferred to Held to Maturity
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				(40,080)	(158,433)
Other comprehensive income (loss) before reclassifications				125,103	169,868
Amounts reclassified from accumulated other comprehensive (loss) income				(12,296)	(16,952)
Net current period other comprehensive income				112,807	152,916
Balance, end of period		72,727	(31,361)	72,727	(31,361)
Unrealized Gains (Losses) on Debt Securities Available for Sale and Transferred to Held to Maturity | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period	[2]				(25,844)
Unrealized Gains (Losses) on Debt Securities Available for Sale and Transferred to Held to Maturity | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period					(184,277)
Accumulated Gains (Losses) on Cash Flow Hedging Instruments
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				91,445	6,175
Other comprehensive income (loss) before reclassifications				313,311	129,110
Amounts reclassified from accumulated other comprehensive (loss) income				(61,767)	2,555
Net current period other comprehensive income		(34,226)	33,662	251,544	131,665
Balance, end of period		342,989	136,800	342,989	136,800
Accumulated Gains (Losses) on Cash Flow Hedging Instruments | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period	[2]				(1,040)
Accumulated Gains (Losses) on Cash Flow Hedging Instruments | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period					5,135
Defined Benefit Plan Adjustment
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				(46,666)	(29,495)
Other comprehensive income (loss) before reclassifications				0	0
Amounts reclassified from accumulated other comprehensive (loss) income				1,754	3,119
Net current period other comprehensive income				1,754	3,119
Balance, end of period		(44,912)	(33,727)	(44,912)	(33,727)
Defined Benefit Plan Adjustment | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period	[2]				(7,351)
Defined Benefit Plan Adjustment | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period					(36,846)
Unamortized Impairment Losses on Debt Securities Held to Maturity
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				(5,771)	(5,095)
Other comprehensive income (loss) before reclassifications				0	(82)
Amounts reclassified from accumulated other comprehensive (loss) income				341	675
Net current period other comprehensive income				341	593
Balance, end of period		$ (5,430)	$ (5,703)	$ (5,430)	(5,703)
Unamortized Impairment Losses on Debt Securities Held to Maturity | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period	[2]				(1,201)
Unamortized Impairment Losses on Debt Securities Held to Maturity | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period					$ (6,296)

[1] Related to the Company's adoption of ASU 2016-02, ASU 2017-12 and ASU 2018-02 on January 1, 2019.

[2] Related to the Company's adoption of ASU 2017-12 and ASU 2018-02 on January 1, 2019.