Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	$ 899	$ 1,059	$ 969
Impaired loans	1	18	16
Level 3 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	1	18	16
Level 3 [Member] | Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	141	191	141
Level 3 [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	1	18	16
Goodwill	$ 979	$ 979	$ 979
Level 3 [Member] | EBITDA Multiple [Member] | Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	5.90%	5.90%	6.10%
Level 3 [Member] | EBITDA Multiple [Member] | Recurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	5.40%	5.50%	6.00%
Level 3 [Member] | EBITDA Multiple [Member] | Recurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	6.00%	6.00%	7.00%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	5.90%	5.80%	6.20%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Recurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	4.90%	5.00%	4.80%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Recurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	10.00%	6.00%	10.40%
Level 3 [Member] | Revenue Multiple (Where Applicable) [Member] | Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	4.10%	4.05%	4.00%
Level 3 [Member] | Revenue Multiple (Where Applicable) [Member] | Recurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	0.80%	0.30%	1.10%
Level 3 [Member] | Revenue Multiple (Where Applicable) [Member] | Recurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	4.50%	5.30%	4.70%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	25.00%	38.00%	36.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	0.00%	0.00%	10.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	80.00%	100.00%	100.00%
Level 3 [Member] | Earnings Multiple of Peers [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input weighted-average	11.59	11.25	11.59
Level 3 [Member] | Earnings Multiple of Peers [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input weighted-average	10.10	9.70	10.10
Level 3 [Member] | Earnings Multiple of Peers [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input weighted-average	14.40	14.20	14.40
Level 3 [Member] | Equity Multiple of Peers [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input weighted-average	1.24	1.09	1.24
Level 3 [Member] | Equity Multiple of Peers [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input weighted-average	1.17	0.95	1.17
Level 3 [Member] | Equity Multiple of Peers [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input weighted-average	1.29	1.17	1.29
Level 3 [Member] | Control Premium [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	35.00%	30.00%	35.00%
Level 3 [Member] | Control Premium [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average
Level 3 [Member] | Control Premium [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average
Level 3 [Member] | Weighted-average Cost of Capital [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	13.00%	13.00%	13.00%
Level 3 [Member] | Weighted-average Cost of Capital [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average
Level 3 [Member] | Weighted-average Cost of Capital [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average
Level 3 [Member] | Impaired Loans [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value measurement, valuation technique	Fair value of underlying collateral	Fair value of underlying collateral	Fair value of underlying collateral
Level 3 [Member] | Goodwill [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value measurement, valuation technique	Discounted cash flow and market data	Discounted cash flow and market data	Discounted cash flow and market data
Level 3 [Member] | Other Investments [Member] | Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value measurement, valuation technique	Individual analysis of the condition of each investment	Individual analysis of the condition of each investment	Individual analysis of the condition of each investment