Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Cash flow hedge activities:
Unrealized net gains (losses) on hedges arising during the period, Before Tax Amount			$ 38	$ (7)
Unrealized net gains (losses) on hedges arising during the period, Tax Effect			(15)	3
Unrealized net gains on hedges arising during the period, Net of Tax			23	(4)
Less: reclassification adjustment for net gains/losses on hedges included in net income, Before Tax Amount			(5)	6
Less: reclassification adjustment for net gains on hedges included in net income, Tax Effect			2	(2)
Less: reclassification adjustment for net gains/losses on hedges included in net income, Net of Tax			(3)	4
Net change in unrealized gains losses on hedges, Before Tax Amount			33	(1)
Net change in unrealized gains losses on hedges, Tax Effect			(13)	(1)
Net change in unrealized gains losses on hedges, Net of Tax	15	(4)	20
Securities:
Unrealized holding gains arising during the period on securities available for sale, Before Tax Amount			147	92
Unrealized holding gains arising during the period on securities available for sale, Tax Effect			(58)	(36)
Unrealized holding gains arising during the period on securities available for sale, Net of Tax			86	42
Reclassification adjustment for net gains on securities available for sale included in net income, Before Tax Amount			(47)	(57)
Reclassification adjustment for net gains on securities available for sale included in net income, Tax Effect			18	22
Reclassification adjustment for net gains on securities available for sale included in net income, net of tax			29	35
Less: accretion of privatization - related fair value adjustment on securities available for sale, Before Tax Amount			(1)	(4)
Less: accretion of privatization - related fair value adjustment on securities available for sale, Tax Effect			1	1
Other Comprehensive Income Accretion of Privatization Related Fair Value Adjustment on Securities Available for Sale Net of Tax				(3)
Less: accretion of privatization - related fair value adjustment on held-to-maturity securities, Before Tax Amount			(14)	(14)
Less: accretion of privatization - related fair value adjustment on held-to-maturity securities, Tax Effect			6	6
Other Comprehensive Income Accretion of Privatization Related Fair Value Adjustment on Held to Maturity Securities Net of Tax			(8)	(8)
Less: accretion of net unrealized losses on held-to-maturity securities, Before Tax Amount			56	52
Less: accretion of net unrealized losses on held-to-maturity securities, Tax Effect			(22)	(20)
Less: accretion of net unrealized losses on held-to-maturity securities, Net of Tax			34	32
Net change in unrealized losses on securities, Before Tax Amount			141	69
Net change in unrealized losses on securities, Tax Effect			55	27
Net change in unrealized losses on securities, Net of Tax	47	69	86	42
Foreign currency translation adjustment, Before Tax Amount			(1)	2
Foreign currency translation adjustment, Tax Effect			(1)	(1)
Other Comprehensive Income (Loss), Foreign currency translation adjustment, Net of Tax	(1)	(1)		1
Reclassification adjustment for pension and other benefits included in net income:
Amortization of prior service cost, Before Tax
Amortization of prior service cost, Tax effect
Amortization of prior service cost, net of tax
Amortization of transition amount, Before Tax Amount				1
Amortization of transition amount, Net of Tax				1
Recognized net actuarial loss, Before Tax Amount			49	25
Recognized net actuarial loss, Tax Effect			(19)	(10)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized (Gain) Loss Arising During Period, Net of Tax			30	15
Pension and other benefits, Before Tax Amount				9
Pension and other benefits, Tax Effect				(4)
Pension and other benefits, Net of Tax				5
Net change in pension and other benefits, Before Tax Amount			49	35
Net change in pension and other benefits, Tax Effect			19	14
Net change in pension and other benefits, Net of Tax	14	8	30	21
Net change in accumulated other comprehensive loss, Before Tax Amount			222	105
Net change in accumulated other comprehensive loss, Tax Effect			86	41
Comprehensive Income Attributable to UNBC	$ 262	$ 314	$ 518	$ 541