Other Comprehensive Income - Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Unrecognized pension losses and prior service costs, tax benefit	$ 20.1	$ 19.6
Unrecognized other benefit losses, prior service costs and transition obligations, tax expense	6.7	6.2
Net Unrealized losses from cash flow hedges, tax benefit	5.8	3.2
TAMPA ELECTRIC CO [Member]
Net Unrealized losses from cash flow hedges, tax benefit	$ 5.5	$ 2.9